The first... /sigh, my baby... my poor baby...
The first, I let the heatsink on the processor get clogged (I run without the side on (as any tech / former tech would)), and given that it had over the past few years, suffered more that 7 lightning strikes (of which I was able to get it running again with a little cleverness), anyway, long story short, one of the many things that I was unable to recover, was the auto power down upon overheat... anyway... heatsink got clogged (as I accidentally fit the fan backwards after I last cleared it), processor overheated, and destroyed the socket in the process.
As for the second... well, frankly I have no idea... I think I destroyed the AGP port after fitting it out with my old components. (it had... 64Mb 3d card, 256Mb ram, 80Gb hdd, which I naturally upgraded with my own components to a 1Gb 3d card, 8Gb ram, and two 2Tb hdd's) etc etc.... anyway, that ran long enough for me to re-activate windows (a mobo is considered a major hardware change), (about 45 minutes uptime and full operations before I decided to do so), then, ran for another 15 minutes or so, and just shit itself. No video, no beep code errors, just... bricked.