Couple of ideas for you, hope one works!
Did this freezing start after a Windows update? If so, uninstall the update and see if that cures it. This may also be linked to a requirement for a BIOS update - some Windows updates (KB numbers) need one. If you know the Windows update which caused the problem, go to the update site and look at the update requirements, a BIOS update may be mentioned.
A remote possibility is a bad sector on your HDD. Run CHKDSK on your boot drive (probably C:).