If you haven't changed anything and this just suddenly started then I'd be looking at hardware not software. Even with a fullyloaded system you shouldn't get freezes for no reason. Nothing is listed in /var/log/messages?
If you do what to try to find out whats going on with your processes you can always run something like
ps aux >> /tmp/someFile
every minute from roots crontab, but this still may not show you the problem as it will use resources itself.