XFX GeForce 6200 LE 256mb DDR2 agp8x Poblem

I have the following config->amd athlon 64 2800+,256mb ddr 400 ram, msi k8m800 motherboard, 400W power supply, win xp sp2 and more importantly a xfx geforce 6200 LE 256mb ddr2 agp8x graphics card(only a heatsink).My processor clock speed is increased to 2ghz from 1.8ghz and the ram and agp volatges are increased by.25volts. I have been using my pc with these settings for over a year without any problems.I have been using all the standard drivers that came with the CDs.Nvidia drivers are 97.1 forceware. Recently I had to format my machine and installed all the original drivers and os as I mentioned earlier and in the same way as I had done 1 year ago(I had assembled my pc on my own).But now while playing games I get coloured vertical lines and dots all over the screen and soon my pc freezes(i can make this out from the stuttering of the sound) and then a blue screen comes showing 'dumping of physical memory....problem with nv4disp.dll', and sometimes problem with ram.I lowered all clock settings to factory defaults,lowered voltages,tried with latest drivers of both my graphics card and motherboard,fiddled with dual monitor support(this seemed to work for 5mins) but nothing helped. My graphics card is fine in vga mode and even while running normal applications its fine.But as soon as any 3d application is run it makes the same problem.Even directx9c tests pass but I get coloured lines on my screen with the dx9 cube freezed.Please help!I dont have much money now to upgrade my pc ti pci-e or buy a new graphics card.I must also tell you that my onboard graphics is fine but sometimes this too crashes which was not the case one year ago.I am student I had need your help urgently.Thanks a lot for hearing my problem and helping.

Try to check your power supply fan if its still working, and also the cpu fan, overheating is the cause of your computer problem, its already 1 year since you build your computer, maybe its time for maintenance, clean the cpu fan and the cpu, and put new thermal paste, and also what game are you playing, if your playing the latest game, then your gpu cannot handle the graphics requirments of the game, try to adjust the settings of the game to minimum and adjust the the display resolution and update the driver of your gpu.