Help

Hi here's my problem. We downloaded what we thought was a safe software and we think we got a virus. When we restarted the computer all we get is a blue screen, no icons. After a few minutes the comodo software will start. We started the scan but it stopped after about 20 minutes. We cannot get it into safe mode or last known good configuration so that at least we can get some function to try to fix it.Hitting the f8 key works but it still goes to the same blue screen. Any ideas?
Thanks