Problem with computer crashing

Hey guys,

I have had a problem with my computer where it will just randomly freeze out of nowhere. It won't do it at a set time that I do something, it is totally random which is making it hard to diagnose.

When the computer crashes, the USB ports will die as the lights on the keyboard and mouse die. It will also just freeze on whatever it is on at the time and not blue screen or anything. (It has also frozen on the POST before)

Now I thought it was my motherboard, so I replaced it. Once the new motherboard went in it has been fine up until today, which is about 4 weeks or so.

I have tested the RAM, put my graphics cards in one by one and without a graphics card, still freezing

This started happening not long after I bought my 80Gb SSD. So I have that to store my OS and 2x1TB HDDs on raid to do the rest.

I thought it would be the SSD but I did diagnostic tests and its fine.

What could be the problem!!! My next assumption would be a faulty PSU?