This could well be memory related, please download this,burn to a cd,then boot from this program
http://www.memtest86.com/ you may need to go into bios and search for boot orders and ensure cd is selected first.If this test shows errors then this would be the problem
If the ram runs a few passes with no errors,download prime95 from
http://www.mersenne.org/freesoft.htm run this whilst online(select just stress testing) then connect to prime net.This test will fail very quickly if the cpu is faulty,I would allow to run for 30 minutes or so at least