Take out the M.2 SSD, 1 change at a time.
The M2000M ought to work if you have the Dell driver installed (unless something has gone wrong with the heatsink reinstallation). If you updated the driver, was it to that or a one from the NVIDIA website? If the latter, try reinstalling the Dell one, should be v 188.8.131.5286 / A01 -- download name is Video_ISV_Driver_33M6J_WN32_184.108.40.20686_A01.EXE for 10 ; v. 220.127.116.1108 / A03 , nVIDIA-Quadro-M-and-P-Series-Graphics-Driver_X1R1W_WIN_18.104.22.16808_A03.EXE for 8.1 ; v. 362.13 / A01, 362.13-quadro-whql_ZPE.exe for 7.
Alternative is that it could be that you got a bum card off eBay, did you check the physical markings that it's the right thing?
Desktop: 750W Snow Silent, X11SAT-F, E3-1270 v5, 32GB ECC, RX 5700 XT, 500GB P1 + 250GB BX100 + 250GB BX100 + 4TB 7E8, XL2730Z + L22e-20
HTPC: X-650, DH67GD, i5-2500K, 4GB, GT 1030, 250GB MX500 + 1.5TB ST1500DL003, KD-43XH9196 + KA220HQ