My Dell Inspiron 1525 won't turn off or hibernate!?

My Dell is a little over a year old, and I've never had any problems with it, but now it won't turn off. If I close it, it won't go in to sleep mode, I can hear programs still running and it will play the start up sound over and over. If I try to hibernate it, it tells me that hibernation mode is not supported. When I hold down the power button, it turns off... but then turns right back on again! The only way I've been able to get it to turn off is to remove the battery, which I don't think is very good for my lappy.