the new computer is up and running! windows is installing on it as i type this.
as i suspected, the problem was that the motherboard was screwed directly to the case. i had to half-disassemble everything to properly mount it & get all those little "motherboard studs" underneath it properly.
if only the coolermaster instructions had actually stated that i needed to use the studs, instead of simply hoping i would properly decipher the tiny illustration.
and while i did solicit some assistance from barry, i basically did it all by myself... and while i did make a horrible newbie mistake, i was the one who researched it and figured out what the problem was. and i was the one who fixed the problem (though i had my sister hold up the motherboard while i installed some studs underneath it).
windows installation will take awhile, and the other software installation will also. but i now have a new notch in my geek belt: i have built my own computer from scratch.