*Help* Blacked out?

Hi there,

I need some assistance with my PC, today, I think I might of downloaded a virus, mainly a trojan. The problem I am having is my whole desktop has gone black, toolbar has also disappeared and when I logg onto my account from the main vista login all that comes up is my documents folder then I need to locate my firefox etc. through there. This is very annoying and I am stumped on what the problem is, any help? thoughts?


EDIT:


*click for larger view*
Picture of the desktop, that may help.


Thanks,

Trey