Ok, I finally have some free time, so I thought I'd post an update. I checked out Event Viewer, and I have to say that it's quite a handy tool. I was able to take a look at an error that was recorded when the computer froze up, when it attempted to enter sleep mode. However, like most of what I found that had been logged, it was inconclusive. It seemed like whatever the problem was, it was embedded deep somewhere in the OS. So, I backed everything up and went ahead and did a System Reset. And since then, everything's been working great! No freeze ups, and the computer seems to enter Sleep Mode without a problem. I'm going to call this issue resolved. I want to say thanks again for all of the help and support! I learned a lot, and I finally have a reliable computer again. Thanks so much!