There might be several solutions for your problem:
1) Memory fault - Check your memory sticks / slots with "MEMTEST".
You may a download links for Memtest in this link:
http://www.memtest86.com/
- A troubleshooting you'll find here:
http://www.memtest86.com/tech.html#trouble
2) Scan your computer for nasty software: Malware / Viruses / Hijackers
- Free Anti-Virus: Avira - http://www.free-av.com/
- Malwarebytes' Anti-Malware -
http://www.malwarebytes.org/mbam.php
- HijackThis - http://free.antivirus.com/hijackthis/
3) Monitor the CPU / Video-Card / Mother-Board / HD temperature.
If one of them get too hot - that's not good and can cause a lot of problems.
- You may use SiSoftware Sandra to monitor these parts - http://www.sisoftware.net/
* Start with scaning your PC for nasty programs. If you got clean results - check the temperature thing.
If temp' is fine - Scan your memory.