Unity crashes for no reason

Hi. I'm using Unity to make particle system for a video game project. At first it worked pretty well, but today, for no reason it keeps crashing every 30sec after i start it. I thought it was a problem of compatibility with a recording video software but uninstalling this one hasn't resolve my problem. Ive upgrade unity to the last version (3.5.2f2). I've got no warning or error message, windows just tell me that the program doesn't answer anymore

My computer runs on win7 x64, 8GB ram, ie7.. I don't if its helping. But that's all i can say about my problem. If someone knows how to fix it, will be a big relief. Thx.