Sleep problem with macbook pro

Hey,

Ive had my macbook pro since july 07 and sometimes when i put it to sleep it never wakes up. The only thing i see on the screen in the revolving beachball or sometimes i see the password entry screen but it wont let me enter my password. My keyboard works when i try to wake it up... the caps lock will light up and so wil the number lock so i know tahts not the case. I recently read something like this in the macbook/macbook pro forum and they said something about istat pro being the problem. I hate having to improperly restart my computer and loose my work in progress. Any advice for me??

Thanks