Given that the problems occur when gaming the first thing I would look at is a possible heating issue. Keep an eye on the temperatures (using software such as Motherboard Monitor), make sure your fans are working properly, clean out your system with come compressed air making sure the heatsinks are clean, try leaving the case open, and even consider using a small box fan to blow air into the case while gaming to see if it makes a difference.
Aside from that I would:
1.) Make sure you have the latest drivers for your graphics card.
2.) Try swapping out the card with a friend's and see if it makes a difference.
3.) Make sure that your PSU can handle the load your graphics card and other components put on it while gaming.
Let us know how it goes.
I have a 3.4ghz Intel Pentium D, 1GB DDR Ram, Nvidia Geforce 7300 GT 256 mb, 250GB HD, Nforce 570 Slit-A motherboard, Windows XP Pro operating system. I played World of Warcraft for about a month and had call of duty, Fear, Quake 4, Black and white 2, also on the machine. I was playing WOW, when the computer locked up and crashed, it kept looping in a blue screen-startup fashion. I ended up formatting about 3 times, because now I can't even install WOW because about 5 minutes into the installation it freezes and causes me to have to restart my machine. I just installed call of duty 2 because I thought it may have been a World of Warcraft problem. I played call of duty 2 for about 15 minutes and it locked up and I had to restart. I was wondering if there is any indicator in there that anyone would know what to do.