Restarting Problem Plz Help.....

Hello everyone, My computer restarts when I am playing World of Warcraft...... It happens at different times in the game sometime I am running or just standing there.... It happens somethimes in 1 min. or sometimes in 30 min. but it does restart. I just put a new power supply in a 550 watt one, and change the cpu fan and heatsink because I thought it might be my cpu overheating but it still does it. I have no idea even where to look. WOW is really the only time it restarts, I have played other games for hours and nothing, but WOW does not want to work right (maybe we were not meant for each other, but I love the game) Please guys and girls can you help me out... Thank you very much for your time....

To further this point, if memtest 86(+) doesn't turn up anything, there are many other system-wide testers and stressers out there to help narrow down the issue, and the best part is all of these testers (including memtest 86) can be found on the Ultimate Boot CD. It's free, just search for it. Keep it with you at all times. Love it.