If you've never intentionally gone into a pornography site, that does show that your machine's infected, though it doesn't actually prove that you're connected to the 'Net.
In principle, with modern infestations, you're going to have to boot somehow without booting your main hard drive, get rid of the infestation, and then return the machine to a state before it happened.
1. What version of Windows are you using?
2. Do you have the appropriate version of WinRescue on that machine? It matters less if you've updated your backups recently, but having WinRescue at least installed would make things easier. If not, don't worry.
3. What removable drives do you have in principle (floppy drives, CD/DVD drives, built-in USB hubs, etc.)?