XPS 8940, random freezing

Random freezing. I've had tech support log in and run hours of diagnostics and of course while that's happening, it does not freeze. But if I am sitting here reading an article with one window open, freeze, have five windows open freeze, in the process of shutting down, freeze. There is no one thing that causes it so I know this must be hardware or factory related. I need this fixed. I spent a lot of money on this computer. Please help.