I did the reinstall a number of months ago with my friend's Windows CD which did not accept the key at the bottom of my Dell, so he let me use a key he found on the net instead. When I restarted my computer today, I got a message from Microsoft that I was using a false key, for obvious reasons.
Anyway, I already fixed the problem and ran KeyUpdateTool.exe and used my own license key. After going through product activation, everything seems to be normal.