Dell Inspiron 5150 boot up problems (bad CPU/motherboard?)

Ok here's the story...my bro-in-law who lives in Spain left his broke down 5150 at home. Apparently, he replaced the motherboard. When he tries to boot the thing up the drives whir and the fan kicks on but nothing comes up on the LCD. Now, I've inherited the problem. I've tried hooking it up to a monitor (to see if it's a broken lcd) but that's not the problem. I've also replaced the video card (cost 25cents plus 9 bucks shipping lol)...that's not it. I've removed everything removable and reseated but no dice (including checking each stick of RAM in both slots individually to see if it was bad RAM). I decided to take it apart to see if he put in the motherboard correctly. When I removed the heatsink, the CPU was attached to the bottom of it (some kind of adhesive)...that's not how it's described in the guide. In the guide it says the CPU is supposed to be held in the ZIF socket by the ZIF cam screw...it appears to be seated correctly, though, when the heatsink is screwed down. Is this the problem? Does the cam screw need to be tightened in order for the CPU to really be seated correctly? I didn't mess with it...put back in the way it was and tightend everything up. I also noticed that the PMI shield was completely removed (what does it do? is it really necessary?)....Any ideas? is it a bad CPU? motherboard? any help would be appreciated...

The lappy is not...he bought it used...but the motherboard he replaced may still be under warranty...i should prolly have him holler bloody murder at Dell for a replacement, huh?