I used to have the same problem, it could be two problems from my past experience.
1. Check that the CPU fan or the ventilation is not clogged up by dust. I noticed that once I cleaned out the dust from my CPU fan, everything went well.
2. Also, it could be due to your RAM. I had one Apacer that wasn't working or had too many error exceptions. Sent it back for replacement only to get a new one to fry it up along with my mobo. I have posted another topic relating to this recently, check out the pictures man!
Hope this helps mate.