OK, usual thorough clean out required
1) reset Internet explorer to defaults
2) clean the hard drive of junk (drive properties > disk cleanup)
3) download and run Hitman Pro
4) download and run in safe mode RKILL (to disable running bots)
5) without rebooting, assuming 32-bit windows, download and run Smitfraudfix (in safe mode)
6) without rebooting, download and run in safe mode Combofix
7) if you know what you're doing, at this stage download Autoruns to go over the startup programs and routines and disable anything "wrong"
8) Now run Malwarebytes (pointless running it earlier)
9) Download and run Spybot Search & Destroy
these are not alternatives - to do it properly you need to run all in sequence