Motherboard not recognising GPU

Until a couple of weeks ago I was quite happily running my Nvidia 9400 GT GPU with no issues. Windows update wanted to update as it does every now an then and afterwards I get a black screen?? I switched to my on-board graphics everything is fine - I try the 9400 and nothing…….. it gets weirder……. couple of days later I turn the computer on again and the 9400 is working again….. does so for a few days then black screen again I've been out today and bought a Nvidia GT 620 and plugged it into the motherboard but even that isn't showing up in device manager. I'm glad I got the new card in any case although bit gutted I may not have needed it but can someone please help me sort this out its driving me insane! Has windows update screwed my machine or am I missing something?? Before anyone tells me to plug the vga cable into the 620 and enter safe mode or bios….. I cant as the screen is black. The fn is turning on the card so it has power, my power supply is definitely man enough so please, please please help me I cant handle my on-board graphics anymore :'( System Specs from Speccy Operating System MS Windows 7 Enterprise 64-bit SP1 CPU AMD Phenom X4 9650 31 °C Agena 65nm Technology RAM 4.0GB Dual-Channel DDR2 @ 199MHz 5-3-3-9 Motherboard ASRock N68PV-GS (CPUSocket) Graphics Generic Non-PnP Monitor @ 1152x864 256MB GeForce 7050 PV / nForce 630a (ASRock) Hard Drives 488.39GB Seagate ST3500418AS ATA Device (Unknown Interface) 37 °C 78.15GB Seagate ST380012A ATA Device (IDE) 40 °C Optical Drives ATAPI DVD A DH20A4H ATA Device UNE KHYBOPUR8 SCSI CdRom Device Audio Realtek High Definition Audio

my power supply is definitely man enough

On paper - but have you tested it to make sure it is properly delivering all 3 essential voltages? Ensuring I am providing quality power to my sensitive devices is one the first things I always do when troubleshooting potential HW issues. If you don't have a PSU Tester (these are not conclusive, but pretty good), swap in a known good supply and see what happens.

I have also the same problem but i take my pc to a professional man who can correct the virus and give me the so after it does not disturb me any more ! B.t.w guys is there any solution to recorrect my hardisk, it was damaged its gold plate was broken ? Thanks !

B.t.w guys is there any solution to recorrect my hardisk, it was damaged its gold plate was broken ?
Thanks !

Are you referring to the gold-plated contacts onto which you insert your SATA cable connector?
Please provide a bit more information about the problem, where exactly it is locate, what occurred, and what functionality has been lost.

Best Regards