hello scott94, and welcome to the forums,
In order to better help you can you give some more information.
such as do you receive any messages or does the pc just freeze?
do you get a Blue Screen error? if so what does it say?
unfortunately your original post doesn't give enough information. although time based problems are often related to screensaver or power management issues.
if you can post back with some more information I'm sure someone will be able to help