With Windows 7,we have had quite a few instances lately with the computers not booting to the desktop, but instead getting just a black screen. Guess what, it's infected!!! But it is fairly easy to fix if you know how to boot to "safe mode" with networking. Once you are in this mode, you can run the clean up tools I provided you in my book. This usually gets it done so you can boot to normal mode. Then run the tools again and you should be fine. Don't forget to run the avast "boot" scan as well.