You may want to make sure all of your components are properly seated. It's possible that something may not be fully inserted into it's socket and therefor is not receiving enough power to operate properly. It may sound kind of insulting to suggest that to someone who knows a bit about computers, but we all make small mistakes sometimes.
Also, make sure that your RAM and CPU are compatible with your motherboard. You may want to check event viewer to see if there are any events that occur at the time the system freezes.