I don't know probably going to look stupid question. But did you check ventilators? Be cause for me was one time as well that freezed and after turning it off I couldn't start it for few minutes. And it all was be cause of ventilator (that suck's hot air from box) was stuck.
[MENTION=8332]samyeung46[/MENTION] check your cpu temp maybe overheat causing that freezing. if safemode works, msconfig disable all your startup programs. if nothing else, a clean install of w7 only takes few hours at most with all your data intact.