Across

2. Puzzle expert breaks first dilemma partially (7)

10. Nobleman bandleader (4)

13. Lead singer, AC/DC's second; extremely over-the-top (5)

18. Actor Morgan and organ lying on the same line (8)

20. Region's stadium has no northern entrance (4)

22. Guide a pharaoh with no money (8)

23. Pose circulated currency (4)

24. Top buck and doe retreat to produce offspring (5)

25. Disorder, cruel disorder (5)

26. Supported university with doctorate about top English literature (6)

27. Nuisance animal's heart removed for blood vessel (4)

28. Crack inside department, shed a tear (7)

31. Truth or part of product (6)

32. Australian river turning west, crossing uptown Melbourne initially, then ending in Victoria (5)

34. King George leaves tussle to tech giant (5)

42. Jump back to front to appeal (4)

43. Scruffy Charles has good game (5)

44. Information desk head at Atlanta's centre (4)

45. Consume boiled heart within city (5)

46. Take revenge for original Google Earth by westward Russian river (6)

47. Step ashore, be back in black (6)

48. Foremost nails' inch number close to Trent's heart (4)

49. Turner leading America's furniture business (4)

50. Without question, prepared to peruse book (4)

51. Meshes of rope turned to weapon (4)

52. Next to nothing, Gellar confused fast (7)

53. Plant seeds stuffing first roots first (4)

Down

1. Half-alien spaceship sent up for food (4)

3. Wealthy, wealthy fictional boy (4)

4. Murder site capital, Warsaw – thunder struck leaders in Poland decapitated (10)

5. Rebel lying to hide abdomen (5)

6. Lap dancing undercover police (4)

7. Set up part of uterus removal (5)

8. Eccentric Sam-I-Am loses last ham to tribesman (5)

9. Cut plant grown for food (4)

10. Debit has no capital interest to money owed (4)

11. Oddly, knife violence capital is European city (4)

12. Heavy metal band is after a heavy metal sound (5)

13. Incapacitate star eating top tranquilizer (4)

14. Stirred alco beverage (4)

15. Fantasy monster atop a whale (4)

16. Sudden death row imprisons every head with time off (10)

17. Pastry evaluated and treated with acid (9)

19. Stride to unopened ramp (4)

21. Grande entrance to arena after returning money (6)

22. Double-headed alien rising, disembodied hand growing fangs (8)

28. Capital also known as cutting doctor (5)

29. Cognitive theorist wants second illustrator (5)

30. Hungarian name is first Caribbean island of Scenery (5)

31. Prenatal cheese not back in black (5)

33. Fictional Kate's counterpart is a two-headed frabrication (5)

35. Use e-cigarette incorrectly to cover road (4)

36. Beige gas regularly breakfast items (4)

37. Lead singer, part of Pink Floyd (3)

38. Absurd need for paradise (4)

39. Childlike ditch, chill ditch (4)

40. Mariner's tale read the wrong way to king (4)

41. Funny lone talk show host (4)

42. Reportedly equal dock (4)

43. Currency fit for a king, no bottom scraping (4)

The finished grid:

Hidden in the grid is

a message reading across the middle three rows: "HELD CAPTIVE IN A CRYPTIC FACTORY, PLEASE SEND HELP".

Clue annotations (gray are unsure / unfinished):

General comments:

- Several answers are obscure: 45A, 51A, 8D, 17D, and 30D were the ones that jumped out to me. You might want to be more detailed in your definitions there.

- Keep your surface in mind. Several had completely nonsensical surfaces: 4D, 13D, and 52A were the ones I noted, but there were others.

- A few places in the grid have two cells in a row that aren't crossed. This is generally considered to be a bad thing, because in cases where the word is obscure -- such as 30D -- it's going to be very hard for someone to actually fill those cells.

Comments on specific clues:

2A, 37A: Both of these use "partial hidden words", where you extract some unspecified number of letters from a phrase in the clue. This can be unfair to the solver because of how many options there are.
24A, 53A: Using REED as a part of the wordplay in a clue while it's also the answer to another is pretty inelegant -- so much so that the National Puzzlers' Leage calls it "The Error That Cannot Be Named".
34A, 50A: "Question" -> Y and "King George" -> GR probably came from the big abbreviation list. This is a useful resource, but has a lot of things that I would consider very unfair, or just plain bad. Use that list with caution.
3D: Both of your definitions here come from the same place. This is generally considered bad style, because solvers won't know which of many synonyms to use -- and even in cases where the synonym is disambiguated, the clue is generally pretty unsatisfying. (43D also has a similar issue.)
6D: Hidden words should be entirely inside the word. Also, the indicator doesn't apply grammatically to its contents -- "X undercover" does not mean "inside X". ("undercover in" would be fine if you swapped the two parts around, though.)
25D: The definition here doesn't work, as far as I can tell - ulcers aren't really a disorder. (I may be wrong here, though.)
35D: This is both an indirect anagram and an ambiguous clue.

10 across:

DUKE (nobleman, thin white duke (bowie))

20 across:

AREA (ARENA minus N, defn: stadium)

24 across:

BREED (B + DEER backwards, defn: produce offspring)

25 across:

ULCER (anagram of CRUEL, defn:mdisorder)

10 down:

DEBT (DEBIT - I, defn: money owed)

11 down:

KIEV (oddly KnIfE + V, defn: European city)

14 down:

COLA (anagram of ALCO, defn: beverage)

Here’s what I’ve got so far:

Across

2: Puzzle expert breaks first dilemma partially (7)

PROBLEM (PRO + B[reaks] + [di]LEM[ma])

18: Actor Morgan and organ lying on the same line (8)

COLINEAR (COLIN + EAR)

22: Guide a pharaoh with no money (8)

TUTORIAL (TUT + O + RIAL)

23: Pose circulated currency (4)

PESO ([POSE]*)

24: Top buck and doe retreat to produce offspring (5)

BREED (B[uck] + [DEER]<)

26: Supported university with doctorate about top English literature (6)

UPHELD (E[nglish] L[iterature] inside U[niversity] + PHD)

27: Nuisance animal's heart removed for blood vessel (4)

VEIN (VE[-rm]IN)

28: Crack inside department, shed a tear (7)

DECRPYT (DE[CRY]PT)

31: Truth or part of product (6)

FACTOR (FACT + OR)

34: King George leaves tussle to tech giant (5)

APPLE (not sure about this one yet)

42: Jump back to front to appeal (4)

PLEA (LEAP with the P in front)

43: Scruffy Charles has good game (5)

RAGGY (RA[GG]Y)

44: Information desk head at Atlanta's centre (4)

DATA (D[esk] + AT + [atl]A[nta])

46: Take revenge for original Google Earth by westward Russian river (6)

AVENGE ([NEVA]< + G[oogle] E[arth])

48: Foremost nails' inch number close to Trent's heart (4)

NINE (&lit; N[ails’] + I[nch] + N[umber] + [tr]E[nt])

50: Without question, prepared to peruse book (4)

READ (READY - Y)

51: Meshes of rope turned to weapon (4)

STEN ([NETS]<)

52: Next to nothing, Gellar confused fast (7)

ALLEGRO ([GELLAR]* + O)

Down

1: Half-alien spaceship sent up for food (4)

TOFU ([e]T + [UFO]<)

5: Rebel lying to hide abdomen (5)

BELLY (reBEL LYing)

6: Lap dancing undercover police (4)

LAPD (LAP Dancing)

8: Eccentric Sam-I-Am loses last ham to tribesman (5)

MASAI ([SAM I AM]* - [ha]M)

12: Heavy metal band is after a heavy metal sound (5)

AUDIO (AU + DIO)

13: Incapacitate star eating top tranquilizer (4)

STUN (T[ranquilizer] in SUN)

15: Fantasy monster atop a whale (4)

ORCA (ORC + A)

19: Stride to unopened ramp (4)

LOPE ([-s]LOPE)

22: Double-headed alien rising, disembodied hand growing fangs (8)

TEETHING ([ET]< + ET + H[and grow]ING)

28: Capital also known as cutting doctor (5)

DAKAR (D[AKA]R)

31: Prenatal cheese not back in black (5)

FETAL (FETA + [b]L[ack])

35: Use e-cigarette incorrectly to cover road (4)

PAVE ([VAPE]*)

36: Beige gas regularly breakfast items (4)

EGGS (bEiGe GaS)

38: Absurd need for paradise (4)

EDEN ([NEED]*)

40: Mariner's tale read the wrong way to king (4)

EMIR ([RIME]<)

41: Funny lone talk show host (4)

LENO ([LONE]*)

43: Currency fit for a king, no bottom scraping (4)

REAL (REGAL - [scrapin]G)

And based on Deusovi’s completed grid, we can find something even more puzzling!

If you take a look near the middle of the grid, you’ll find the phrase “HELD CAPTIVE IN A CRYPTIC FACTORY PLEASE SEND HELP.” I hope the OP is ok...