Pc wont shut down..

Hello,
can anyone tell me whats wrong with my PC i have win Xp and it wont shut down or reboot it`s going on untill i see message " Windows is shuting down pls wait.. " and it freeze there so i must forse shut down with the on button.. i`ve clean register , scan pc with AVG 8.5 , repair windows with windows cd , scandisck , made shortcut on desctop to force shut down with " shutdown.exe" and i got nothing i still can`t shut down my notebook properly

can any one help me to resolve my problem ??