This is probably a hardware error (probably your RAM). Go here:

http://www.memtest86.com/

download memtest86, follow the instructions that come with it, & let it do as many passes as you can (leave it over night if you have to).
If it finds any errors, you know its the RAM (check each stick seperately if you have 2). Replace the faulty RAM stick.
If you have no errors its obviously something else.
Good luck