Sweet thanks. Lock ups like this can be incredibly difficult to diagnose
As far as the event viewer goes, when it opens, in the top left section select windows logs and then select the system option. It will be a daunting list, but it is all in chronological order, so next time you get a lock up, note the time and check the logs for anything critical (red exclamation point), but also note any warnings (yellow exclamation point) leading up to it as well just in case. This way we can try and figure out if there are any hints as to whether this is hardware or software related, I'm leaning towards hardware since your windows reinstall didn't help, but we can get hints from here that might point us in the right direction.
In the meantime, make sure all you drivers are up to date, and listen for any odd noises (like a clicking sound from your hard drive) coming from your case. You can run it with it open to do so.
Another thing you can do is run memtest on your RAM, the website should have instructions on how to use it, but if you have any questions or you don't understand something just ask
http://www.memtest.org/