The same exact thing happened to my computer on Thursday. I managed to get rid of the blue screen with the trojan's name that replaces the desktop, but now I have a blank, light blue screen, but I did manage to get rid of the trojan. I still haven't gotten my desktop, taskbar, start menu, etc. back. In Google, search for 'Trojan-Spy.HTML.Smitfraud.c'. You should find something to help you get rid of the trojan itself, but other than that, I still don't know how I'll ever get my desktop, taskbar, and start menu, etc. back.