Hi there hawthe,
I would agree with hang-the-9. There's a chance that your HDD is failing. Just back up the data stored on the drive and test it with some of these:
http
/www.tomshardware.co.uk/forum/282651-32-best-diagnostic-testing-utility
If the HDD is in a healthy state, then you can boot into safe mode and see if the issue persists. In case it does, then most probably, there's something wrong with a hardware component. It may be a good idea to take it to a repair shop, or to contact the place you got it from. (if under warranty)
The the laptop works just fine when in safe mode, then a clean OS install might fix the issue.
Have you cleaned the dust out of it recently?
Cheers,
D_Know_WD
