Random freeze up, can't find the cause and a solution

Hello, I'm having some problems with my computer.
Sometimes it freeze up and I can only hard reboot it, mouse and keyboard doesn't works(audio sometimes works and sometimes it stops). I had this problem with windows 7 too. This problem is very random and I had it for a long time, it can happen every day in a week or just once in a few months.

I've run memtest86+ and didn't show any problems (I stopped it at 15 passes). Also checked my HDD and SSD but they were fine.

What can I do?

One of the first things I check when confronted with sudden/random/unexplainable issues, especially with older and not-so-old motherboards, is for bulged and/or leaking capacitors. A number of board manufacturers and power supply manufacturers got capacitors that had manufacturing problems that didn't show up until the devices had been in use for awhile, sometimes a year, sometimes 4 or more. I've junked 3 computers in the last 2 weeks just for such a cause. The years span mentioned at the beginning of this article is only for the manufacturing, failure could happen when the computer got even older:
Capacitor plague - Wikipedia, the free encyclopedia

64bit.
My GPU is external, tomorrow I'll try using the motherboard instead.

The problem is I had the same problem with windows 7. I can try using Linux and see if I the problem persists.

I checked the capacitors on the motherboard but they were fine (none were broken, none were bulged, and none had "rust" on them. I've also taken some photos, tell me if you want to check them).