This will be short, I'm at work and therefore not supposed to be on here.

I have WinXP..home?

For a while I JUST had wallpaper. No taskbar and no icons. I had to get into everything thru ctrl alt del.

I ran MB overnight as superantivirus kept freezing and AVG Free 8. something would not run at all.

It had 400 some finds. So I rebooted.

Now when I try to get on my computer the log in screen comes on. Didn't before.
I click on a user, get a nanosecond of wallpaper then POOF logging out.
It does it in safemode as well.

I have tried every option by doing F8 at startup with same results.

More than likely USERINIT.EXE was infected and removed. You need to restore that file from the Window XP CD

And if I cannot find my CD?

Then try to borrow a friends CD or at least try to burn the file from a good working computer to CD and then you will still need either a bootable XP CD that you can use recovery console, or take the drive out and slave it to another and copy that file back.