I was running 10.5.8 on both my white MacBook and Intel iMac 20," then I finally received the copy of Snow Leopard which I bought from Amazon. I decided to install it on my MacBook first to make sure the install would be successful before I upgraded my iMac, which has my important work stuff on it. The install was a success on the MacBook and after it was fully upgraded and updated, I simply opened "About This Mac" to verify the installation, opened Safari, browsed around for a minute, then proceeded to check out the new dock and airport menu features. After just a few minutes of playing around with it, I decided it was a legitimate installation, closed the MacBook, left it plugged into the power source, and walked to the other room to begin the upgrade onto my iMac. I left home for about an hour and once I had returned, the iMac installation was complete and it was running like a dream. After messing around on the iMac for a little while I decided to make sure the MacBook was still good to go. When I opened the Macbook up, all I saw was a blank screen. I assumed it was some sort of power-saver issue, because sometimes the screen doesn't like to come on right away when I open it up. My first instinct was to move my finger around on the trackpad and press some keyboard keys, which always wakes it up when this happens. Nothing seemed to be working, so at this point I pushed the power button and it proceeded to boot. As it began to boot I heard some sort of CLICKING from the HD, followed by a flashing folder with a question mark on the screen. I assumed it was some sort of HD failure so I booted to the Snow Leopard install disk, ran Disk Utility and Startup disk, and my Mac COULD NOT FIND the HD - all it showed was the CD-ROM drive and Network Startup. I tried to reboot a few more times and almost gave up. It kept clicking at startup and I was thinking about the little magnetic arms in the HD. I thought they might be jammed in the HD for some reason. At this point, I didn't know what to do. So, as it was booting up again with the plain grey backdrop, as a last resort, pretending I was the Fonz or something, I physically whacked the area on my MacBook near the power button where the sound of the clicks was coming from. AS SOON as I did that, the clicking stopped and a few seconds later the APPLE ICON appeared... instead of that dreaded question mark folder icon! The MacBook started booting up back to it's upgraded self again! Finally I was back at the desktop, and with a sigh of relief, began typing this forum. Now, my question is WHAT THE @#$% HAPPENED?? And how on Earth did smacking it one actually fix it? Is this problem related to the recent installation of Snow Leopard or just my MacBook dying? (It is 2 years old) If anyone has any ideas as to what caused this, and how I can prevent this situation from happening in the future... please reply. Thank you!!!