A sudden restart could be because of the serious error. XP detected something was wrong and shut down. To prevent further problems...When the error log is completed it will send it to Microsoft where it will tell you what the problem was (if its known) and a possible fix.
Log on as Administrator.
Go to Start > Control Panel > Administrative Tools > Event Viewer > Look at the "Application" and "system" logs.
Look for red circles with an X in them (ERROR).
If it hasnt happened again and your computer is running fine - dont worry.
As for the picture in the start menu. Right click the Taskbar > Properties > start Menu > classic start menu...
(Not sure if you can remove the picture from an XP styled start menu)