Dell Latitude D800 boot up problem

After a normal shut down my laptop won’t boot. It begins to power up, the lights flash and then it just shuts down. The interesting thing is that if I put just a little bit of pressure above the keyboard on the left hand side it boot up runs normally, but when I remove the pressure it locks up. I have checked for loose screws, etc. but nothing seems out of the ordinary. I am worried that it is my motherboard. Any thoughts?