Unity freezes my computer

After about 30 minutes of using unity my computer will freeze up completely. It’s not overheating or anything, and the only thing I can do is cut the power. I don’t have this problem with any other applications or heavy games, so it’s not because my computer is too old to handle unity.
I’m using the latest free version of Unity and Windows 7 64 bit. I got the newest drivers for my hardware too.

My computer:
i7 920 CPU
GTX 295 videocard
6gb ddr3 ram

Anybody else have this problem? It’s happened 4 times over 2-3 hours now, it’s my first time using Unity.

I have the same problem with Unity 5.3.4f, if your problem is fixed someway could you share it with me?