Can load bootloader but not OS?

I disassembled my Eee 900 HA yesterday because the fan was making some noise. This required taking the whole motherboard out and everything because the fan was at the very bottom. I reassembled it and everything seemed to work fine (although the fan still makes noise -- I think it's a bearing or something like that).

Then, this morning, I accidentally put *slight* pressure on the left side of the laptop in front of the keyboard. The screen went black (the backlight turned off too), and I was forced to restart. But now, every time I restart, the screen goes black as soon as the bootloader loads the OS (or earlier, if I put pressure on the left side of the laptop). I'm running Ubuntu 10.04, so my bootloader is GRUB. The GRUB menu comes up fine, and I can use the GRUB command line for as long as I want. But if I tell it to load a kernel (or even run Memtest86), the screen goes black. If I tell it to run Memtest, I can see the blue Memtest screen for a fraction of a second before the screen turns off.

I have NO idea what's going on. Any ideas? It's not a problem with the screen itself or with the OS; I've already ruled those out.