I hate to tell you this, but the only way I was able to successfully unfreeze a MAC is to turn it off and then back on, which, unfortunately, caused a loss in data. The only time I remember my MAC locking up was because of a particular piece of software. That was Quark Express. If this was the cause I strongly suggest you trash Quark Express. I had a MAC at home that did not have this software and it never froze. I used multiple MAC at college and in a job. All of those had Quark Express. They all froze while I was using Quark Express.