If this frequent the the 1st possible cause a failing hard drive -
It could aslo be simply that the Operating/registery and much else is full of errors
So the fisrt course of action is to do a good cleanup -depenting on what software you have available.
Go to Start/Programs/asccessories/System tools
and click on disc clean up.
Then click on Defrag.- if you have never done a defrag it could take a long time.
best done at night before you go to bed and come back to it next day.
If you have access to Norton Works or Ashampoo
these are clean up programs that do for you do the work with these