Does it work if you type URLs? Do they appear to change when you click on them?
I'd try a Spybot S&D and Ad-Aware double-dose and see what happens. Smells like malware to me, just to start.
And if it is, I'd change every password you entered while you were *ahem* afflicted. Nothing more fun than having someone hijack your account...
If that's not it, respond back with more details about what exactly is happening. What do you do, how do you click or enter, and so on.