Computer Randomly Hangs And Returns To Normal

I've owned my custom computer for about 3 years now, done various upgrades on it. But now I don't understand what's happening. When I play Games or doing normal browsing, my computer will hang and everything will freeze for about a minute or two. It's more when I play Video games than when I surf the internet. It then returns to normal and I can do whatever for the next 10-15 minutes, and then it does it again. I tryed to get past it but it starts to do it more frequently.