do you have Ccleaner
go to tools/start up and see what looks "weird" viruses usually have names like fnjfi39rjc or such.
choose "disable" and reboot. if you have no problem from disabling it in the start up menu, look where that file resides on your hard drive and delete it.
bub bye nasty pr0n site virus.
now it may have also gotten into your registry, that is a little more difficult to deal with