Thanks for the suggestion about a possible short circuit. I was going over the issue with another TR aficionado friend over the phone, and he suggested the same, but we confirmed that this wasn't the case.
As far as I can tell, the 4-pin fan that came with the CPU cooler will not work with the dedicated 4-pin CPU_FAN header, but will on another generic 4-pin header. I grabbed a 3-pin fan of the same size and connected that to the 4-pin CPU_FAN header and it worked perfectly. So I mounted both fans on the cooler tower and that seems to be that.
That in and of itself didn't resolve the system hanging issue, so I took everything out save for a single RAM module, CPU, video, and keyboard. Finally, a successful boot attempt (no HDDs attached). After testing one by one, I was finally able to reconnect both RAM modules, my PCI sound card, PCI wireless card, and three SATA hard drives. The only thing different between my first attempts and the current successes is the detachment of front panel eSATA connection, but I don't see how that would prevent a system hang. Maybe I just needed to reseat something, haha.
It seems I just have to do without that and speed-control on the CPU fans, neither a big deal for me.
Thanks again for the assistance!