Stuck on Blue Screen After Software Download

Hi,

I downloaded a screen dimmer app and somehow got Mac Keeper instead of the app I wanted. I deleted that and then downloaded the app I wanted but an audio commercial started playing during the installation process. The next day the computer wouldn't start up and got stuck on the blue screen. The disk checks out OK in Disk Utility. I also started in safe mode and did fsck or whatever that is. I reinstalled Snow Leopard but I am still stuck on the blue screen on start up. Please advise. Thanks in advance,

Mike