I think you've been hijacked by one of the Babylon toolbar exploits
Usual answer: one by one in sequence
delete all temp and temp internet files
run TDSSKiller
run RKill
run Hitman Pro
run Smitfraudfix (if 32-bit OS only)
run Combofix
scan with Malwarebytes
scan with Spybot S&D
see what happens
You may need to reset the Windows or IE shells - post back if you still have a problem
What antivirus / security software do you have on the machine?
Whatever it is, it didn't work