Gotcha.. so it still is in sleep mode when you reach the desktop... So the keyboard isn't available. I thought it was just Explorer.exe not starting up.
You can safely delete the Hiberfil.sys file... this file saves the system's state, open files and programs... saves everything as they were at the moment the system went into sleep mode... so deleting it will only lose the state of the system and possibly unsaved data but other than that no harm can be done. Hiberfil.sys has been always a problem possibly due to corruption, so it's good practice to delete it or disable Hibernation occasionallty to renew Hiberfil.sys, so deleting it is not only not harmfull but recommended to prevent situations such as yours.
Ways to delete it are: from the Recovoery Console (Windows XP Installation CD), from another system, (the hard drive as slave), from a Live CD (Hirens Boot CD), through a network, etc.
It's hard to tell if a virus is involved, you have to get the system running, then you can run virus & malware scans, or you can download an antivirus in Live CD and do a previous scan.
Anti-Malware Rescue CD and DVD
http://www.malwarehelp.org/anti-malware-bootable-rescue-cd-dvd-download.html
Three Live CD Antivirus Scanners You Can Try When Windows Won’t Start
http://www.makeuseof.com/tag/live-cd-antivirus-scanners-windows-start/
Recovery Console
http://www.windowsnetworking.com/articles_tutorials/wxprcons.html
Recovery Console Commands
http://commandwindows.com/recovery-console-commands.htm