OK you should do this:
- Download, install and then run - - PerfectDisk - - to defrag all hard drives and partitions
- Once its completed the defrag, reboot your pc
- Check your hard drive for errors by clicking on the vista start orb and then clicking on Computer. You then right click on your hard drive and click Properties. Next go to the Tools tab and under Error Checking click on Check Now and tick both the boxes. Then click Start and reboot your pc
- Check you RAM for errors by clicking the vista start orb and typing in the search bar MdSched then hit enter then click on restart now.
I think it may be a problem with your RAM so it would be a good idea to do the above steps just to make sure there are no hard drive or RAM errors.