Try this: Switch all power off and unplug mains AC adapter. Take the battery out. Press and hold in the Power button for 30 seconds (to drain any residual current and clear the voilatile memory).
Put battery back in and AC adapter, plug back into mains electric. Switch laptop back on and see it if works now.
Tip for future use (in addition and separate to above) sometimes it is the AC adapter plug into laptop that works loose and doesn't make proper contact. Oh and also make sure the fan outlet is clear of dust and fluff :)