Yeah, it's the Ye Olde
Siemens A100 ADSL USB modem.
I'll try unplugging it and playing something. It's worth to try. I don't play online games, so it's not a big deal.
EDIT: Well, been playing DAO for an hour and no BSOD, knock on wood. I'll keep testing tomorrow.
EDIT2: Hmm BSOD's again this morning. DAO managed to run for 20 minutes before crapping out, and Skyrim barely managed 5 minutes. Maybe it really is a heating issue. I guess I'll wait until the weather settles down a bit and see if anything changes.