If you are experienced, disassemble the unit and look for any loose connections or broken components. If any of the solder joints has cracked or broken though (eg, under the Northbridge), then there is probably nothing you can do about it but to get a new motherboard. If you have important data in the laptop i would suggest to make a backup before attempting anything else. In case you wonder how to do that since your laptop is not working, take it to a computer store, where they will take the hard drive out, backup your data on another medium and you are ready!