Preventing my computer from restarting automatically b4 my setting

[mils]

When my computer is getting ready to load my settings(icons) the computer
automatically shut down and restarts about 3 to 4 times before it actually
loads my settings. What can I do to prevent that from happening everytime i
turn my computer on? I have windows xp profressional version 2002, service
pack 3. This problem started to occur after i recently installed a new
anti-virus (AVG). One of the errors mentioned updating BIOS, which i did one
time, however, the problem was happening before i did that. Sometimes when i
am shuting my computer down i c a notification saying ending program-Virus
definition missing. Also my computer is refurbish (OEM)

 

[Richard G. Harper]

The first thing you should do is post this question in a Windows XP
newsgroup as this one supports Windows Vista.