winxp shutdown, sleep or hibernate problems

i am using win xp on my laptop acer aspire 5920. recently i had formatted my pc and this is the first time i have formated my laptop in last 3 yrs. i am facing a new problem whenever i shutdown the laptop through the regular process i.e. start-turn off computer-shutdown the sysmtem dosnt get shut down. i have tried 100 times. once i kept it on at night and next morning when i came it was still shutting down. same is the condition when i pres the sleep button or hibernate the system.

Please guide me.

thanks.