Windows 7 Random freezing Please help

For testing purposes I would suggest taking the side off the case and using a floor fan temporarily to help dissipate the heat and enhance airflow.
If that resolves the problem, then you know what you have to do, which may include purchasing another case to better facilitate cooling and the addition of more fans.
Be careful when adding fans and the direction of the airflow, everything blowing in does not help anything. You must exhaust the warm conditions inside the case, and if the PSU fan is the only fan exhausting, then it may not be up to the challenge.

Well, for the CPU you can't really put another fan in. The important part is to have the fan clean from dust, as well as the metallic part = heatsink, which is in contact with CPU itself, between the fan and CPU take a search with "heatsink". In order to do that, you need to remove the fan, and preferably the heatsink too - when loosing the heatsink you should clean it, also from old heatpaste = paste that gives a true contact with the CPU, since they aren't 100% suits. Replace it with new heatpaste. NOW this may all be slightly problematic, thus I recommend DON'T do it, if uncertain. And I do believe your problem is Mobo temperature = result of common case warmth.

But still, you should clean your CPU cooling now and then, depending on circumstances, at least every six months - if you live in a desert area, you have more dust, and vice versa. In Africa, where the comp temperature is 40 degrees Celsius at start, since air is 40, problems are quite different from Greenland, where start temperature may be -40 degrees Celsius. In comes condensation, elephants and ice bears... whatever?

With the general case part, fresh air in from bottom, rather through a filter to get rid of dust, and hot air out from top. Trouble gives a sound advice.

I've thought about building a computer inside a small fridge, style minibar, to keep it cool and quiet. But the condensation would probably be a problem. One engineer, asked what he would do to control both heat and noise, said: "I would sink the computer in a barrel and fill the barrel with concrete. MASS transfers heat, and MASS prevents noise."

Go figure?