roy69

Try running chkdsk on your harddrive.
Run a memory checker.
look at your error logs;

Left Click on Start Menu.
Right click on Computer and choose manage.
Click on the event viewer.
You now have loads of options to try and pin down what is happening.
Expand the error tab.
Look for things in the last 24 hours.

Also look at your reliability and performance option.

Let us know what you found and we will start looking from there.