Cant get Rid of a virus

I have somethin on my computer, when my pc starts up it just goes blank, just shows the desktop, no icons no start menu nuthin.. to get into any kind of pgms, I would have to open taskmanager and do it that way. I have looked everywhere as to how to get rid of this, and so far have run about 5 diff virus protection pgms, and nuthin has worked. I have defraged my pc, and did everything I can think of. And now my computer wont even open programs with the taskmanager.. its worse than it was before, pretty much turns on.. but has nuthin on it.. can anyone help me?