Corporate IT will tell you this:
1) Unplug your computer from the internet
2) Boot in to safe mode
3) Back up your data (USB drive, DVD, etc.)
4) Wipe the computer
5) Install a fresh copy of Win
Sorry you got hit with those pesky type ads, but I've worked in big corporations a long time and once a computer is infected it's always suspect.
For anti-virus at home, I use Windows Security Essentials. Free, painless, and has been working like a charm. And, it's top rated too.