Well, as additional troubleshooting steps try to remove the HDD and DVD-ROM (HDD is usually under a different panel on the underside and there should be a screw that holds the DVD drive. Use a pin inserted into the small hole in the face of the DVD drive to pop it open and pull it out.)
Then start up in this condition, just to see if you get the BIOS. Also, have you started with only battery, or only adapter?