Confused and concernd

Hello,
ive just downloaded norton antivirus on to my desktop computer with windows xp and restared my computer afterwards,but when it started up the desktop and all its icons including the start bar all disapperd.i left it but nothing showed up but it was responding to me alt-ctrl-del to bring up the task maneger so i cut off its power and tryed it again but the same thing happend.so i tryed agaain and all was fine...so whats caused this? and how do i fix it...and can i get a download for windows xp reboot that will go on a cd how and were?

thanks confused teen