My computer Will not start

Hi, I was watching a video in Mecachafe and then my computer got something that would open firefox every 30 seconds with a popup. So when I did the scan It found the problem but said I needed to restart the computer to take effect. So when I restarted and got to the part that said "Windows Xp Home Edition" the blue bar stoped and the computer restarted. I told my Math teacher about the problem and he said It was drivers conflicting with each other. So I dont know how to fix the problem. PLEASE HELP!!!

What did the pop up say?

What did you scan with?

Have you tried booting into Safe Mode and scanning with your anti-virus?