Viruses won't allow antivirus to run

My computer is saying I have many viruses. I cannot run any antivirus programs, and cannot open dowmloads. I updated the software that this site requested, and tried to run winlogon, but it says it is infected. If I try to go into add/remove programs, it says the same. I'm not sure where to even start.

Please visit this webpage for a tutorial on downloading and running ComboFix:

http://www.bleepingcomputer.com/combofix/how-to-use-combofix

See the area: Using ComboFix, and when done, post the log back here.