I bought my ATI HD 4850 2 years back and it was running great till last month. About 3 weeks ago the display would go blank after 5 minutes of starting of the windows but sometimes the display went blank after 1 or 2 hrs. But since last week it's not giving any display. I am now using my onboard graphics for work and still wondering about the problem.
I have tried :-
1.) Disassembling the whole computer , cleaning up everything including Graphics card and assembling it back.
2.) Reinstalling ATI drivers (Updating also) .
3.) Setting the Default display device to PCIe in BIOS.
4.) Checking all the wires,cables and connections.
My PC Specs are :
Motherboard: Intel DG41TX
CPU: Intel Dual core 2.0 GHz
RAM : Kingston 4 GB DDR3 1000MHz
Video Card : ATI HD 4850 1GB
PSU : Coolermaster RS-500 (500 W supply)
Monitor : Samsung BX1931 LED Display 19"
Hard drive: Seagate 1TB
Sounds like the gpu has died. It could be over heating make sure the fan is clean and spins easily with your fingers. Also look into the air channels to make sure they are not caked with dust. If all looks good try installing it in another computer like JSC suggested.
its sound like your card may have over heated
if you have a spare machine or a friend with another computer you may be able to try installing the card in a different computer and if the screen still is black or goes blank after a few minutes then it would be the card has overheated or has some possible heat related issue. and since your computer still works with the intergrated grafix then it most likely is the card.