Windows freezes up

I turn my 6 month old VAIO PC on and everything runs
fine. After the computer has been in hibernation mode or
if the screensaver has been on for a while is when I
experience the problem. I try to run a program or get
online and the windows start freezing up. The only way I
temporarily resolve this problem is by using the the Task
Manager to end all applications and then end one process
at a time until all the windows close and everthing seems
to be working fine again. This problem started a week
ago so I restored my computer's settings to two months
ago. This attempt didn't resolve the problem. Any
suggestions of what I may try next?