system instability can happen when ram isn't paired correctly. its strange to see a computer with 3 ram slots but I know they exist, but if all ram slots are filled with the same exact stick it shouldn't be this problem.
that error in the error report is a BSOD, it might be flashing too quickly for you to notice it. you can force it to show by going to
Right click my computer, Properties, Advanced, Under startup and recovery click settings, In the new window un check automatically restart.
reading this article may help
http://www.maximumpc.com/article/fea...survival_guide
Memtest86 is great, and you should be able to run it off a usb stick, but burning it to a CD is just quicker, it literally takes 20 seconds.
My PC has random BSODs about once a week, but since I use my laptop now for everything, and just that one for my tv shows. I have no real reason to get to the bottom of it.