It might seem obvious, but is the chipset the updated B3 version? Either way, it could be a sata controller issue though I would certainly also take a closer look at the ram.
Good thought checking since I didn't specify, but this was purchased from Newegg just a couple months ago (I understand the faulty chipsets were yanked out of the channel quite early this year), and the box does specify "New H61 B3 Revision" on a red banner. Since I got Windows up without error this time I tried downloading SC2 again, and ~75% through saw a data verification error appear in the status. Would bad RAM affect a download being written to a file? I understood that DMA had been bypassing that for quite a few years. I can download and run Memtest though in any case.
I honestly wouldn't be sad to get a new motherboard; the X68 would have enough fan headers to remove a TON of cables from the power supply and clean things up immensely. I just don't want to get the wrong thing and still have a busted computer.
Thanks all! I'll post after Memtest runs a while. Is this the most current/ correct version?http://www.memtest86.com/download.html#R40a