Inspiron 9100 Motherboard failure?

I've got a Dell inspiron 9100 and I know have some sort of hardware failure. I'm leaning towards the motherboard cause I've tested all the other components  in another system except the motherboard and video card. a couple of months ago I noticed that when I'd move my laptop it would lock up, the harddrive light would get stuck on and you'd hear static from the speakers and then the screen would go black. then when you went to turn it on it would leave all the lights on for a second and shut off. I found that if you whack the palm rest right right it will boot but it won't get past the load screen on any os. I can't even get the diagnostics disk to load. I had a similar problem in my inspiron 8200, and it turned out to be the dc power board kept comming loose, but the 9100 doesn't have one that attaches to the motherboard. I've removed the motherboard and visibly inspected it as well and I see no loose components or damage of any kind. I'm about to fork out the $100 to get a new motherboard but I wanted to make sure that the motherboard really is the problem. when it won't turn on I've even tried taking the battery, cd, and harddrive out, or used the battery and no ac and it doesn't change the problem. only the whack will seem to get it to turn on at this point.