Since Laptops have internal power, the windows Power Saving and BIOS features may be different from a tower.
What changed?
Do you use Hibernate? Sleep mode? just close the lid? Hybrid sleep (W8) Get keyboard wet?
Can you shutdown using start menu or Metro or whatever and repeat the problem?
IS Lid open when this occurs?
Control Panel has different options for AC and DC power mode under Power Settings, also in BIOS as Brad suggested for towers but not usually mobiles , I suggest.