My computer has been giving me errors about how memory failed to read from such and such places (long string of numbers and a few letters), and caused the program to terminate. Also, sometimes I get a blue screen which tells me it has dumped the memory. I must pull the power cord out of my computer and restart. A couple times now, after this has happened, I am informed that my computer has ‘recovered from a serious error’, or similar message.

What are the possible problems? I do not have any viruses or spyware/malware on this computer. It's happened maybe one or two times far in the past, but this frequent crashing started a week, maybe a few weeks, after installing a new graphics card. It has been getting more and more frequent. I've had the card ~4 months now and it is happening many times a day at random unpredictable intervals. How can I tell if the problem with with my RAM or the card?

 

Currently I'm running an ATI X800 card.  I know that this card is fully compatible with this system. If I am forced to replace it, what is the best card my 8400 could handle? My PSU has been replaced with a 470w.