Have you thought that it could be your memory modules?
If you have two, take one out and run the system for a while. Then do the same with the other one. If you only have problems with one, then it's faulty and you need to replace it.
If you only have one module, can you borrow one from someone, or do a temporary swap to try and find out if the other person gets the same problems.
If this doesn't help, it could be motherboard related.
On the other hand, it might be swapfile memory, so you may have some bad blocks or other sorrupt areas on your hard disk.
Hope this helps.