Ok here's what you need to do.

Go to http://www.lavasoftusa.com/software/adaware/ and download the trial of ad-aware.

Run it, that will get rid of all the nasties causing random pop-ups.

Turn off or remove your popup blocker, its probably not the one you want anyhow.

Try registering again, (after a restart and making sure your browser options are right.) Then it should go fine.

After that, research selective pop-up blockers, some are pure Best if kept off the board, I use none at all due to my firewall+net security pack taking care of them.

good luck!