Does this happen whenever the laptop is unplugged?
It could be a few things, check your power settings and make sure it is setup the way you'd like it to work.
And second, it is possible your battery is loosing its charge, if this is the case, you would have to purchase a replacement.
Also, this post would get a quicker response if it were made in the right location.. maybe the hardware forum.
Modz, Do you magic!!
EDIT: WOW, that was fast!! Good job Modz (moving thread)
Youre welcome bud