Harsha Vardhan's answer is the intelligent and helpful one, and will probably suffice. I add this reply in case your question is dealing with the motherboard more directly (?). If you have the laptop open and have been working on it, there is an internal CMOS coin-type battery which holds BIOS settings when the laptop is shut off. That battery can generally been unplugged, which will reset the BIOS to its defaults. If the BIOS won't hold settings, the CMOS battery may need replacement. If you've accidentally somehow damaged the BIOS, a very few BIOS chips store a backup of the previous BIOS version which can be restored. Most do not. Reflashing a 'bricked' chip is a problematic (read: complex and expensive) matter, although it can sometimes be done. Whew! That's enough!