Windows XP taskbar and desktop has disappeared

I have Norton A/V up to date.  I turned on my laptop this morning and it's started without my desktop, and without my taskbar.  While puzzling this, the window came up that Norton was performing background tasks.  Looking online, this problem appears to relate to a download or something, but I hadn't downloaded anything shortly before this happened. 

 

Can you give me any instructions?  All I can do is navigate with the Windows task Manager to open .exe files, but I can't search for them, so I'm digging around ineffectually.  I can't even open My Computer ...

 

Can you help?  If this is a virus, why didn't Norton pick it up?  I'd like to run a full system scan, but can't tell which of the .exe files in the Norton/Symantec folders is the one I need ... I'd be grateful for a steer on this too (installation was your default folder structure).  Thanks.