update 2: pressing down on the heatsink did the job. as soon as i let go, the screen went blank. this leaves me with two questions:

1: did i actually press the gpu against the mainboard, thus connecting something that's loose, or did the motherboard sink deeper into the tablecloth, thus separating itself from the chip? the former is, of course, much more likely.

2: why is it that sometimes there's no hd activity on powerup, and if this happens when booted, then why can't i hear the sound up/down feedback sound? i'm guessing sometimes the machine completely freezes because of an incomplete connection.

anyway, i'm sure now that this has something to do with the gpu. i have to get some sleep, but i'll try it again in the morning.

this is really exciting in a strange kind of way.