|I should lean towards blaming hardware, since the problem occurs only during power up/down, right? How could Mint keep the PU from shutting off (even after the OS has seemingly shut down(i.e. no CTRL ALT DEL helps)), or then keep it from turning on when it is off?|
I did find a small paper label with a barcode and this number: UY30946134125 PC G41S-K, with the G41S-K matching a motherboard search on newegg.com.
Oddly, I went and looked at my partitions, and there were a couple of issues (including a bootable swap partition) that were just odd. Somewhere in my panicky re-installation of Mint, I suppose I just scrambled the HD a bit. I did a complete wipe and install, including reformatting the entire HD, and everything seems to be working normally again. Thanks for the help, but I'll label this solved.