Chances are your system is so corrupted/comprimised that nothing short of a re-install will fix your system.
I would backup User data files to DVD's (do not backup to an external or dvd that contains other data as chances are good the data you backup will be infected).
then If possible run these (to remove the malware if possible, and hopefully without data file corruption*): Avira Antivir
(downloadable free software)
Avira is one of the best Antivirus vendors on the market. ((AV-comparative
(Alwil) (downloadable free software)
Free Home Edition antimalware progam. Malwarebytes.org ESET SysInspector
* alot of polymorphic malware (trojans) alter the files, and when they are subsequently "cleaned" it damages the file, and corrupts it.