Thanks for your advise dertien! SHIII rebooted my PC again after my last post in this thread, so it probably was not even the disk space. After reading up on the error it seemed like it was related to drivers and I figured it must be the gfx card since my drivers for it were really damn old, for the reason given in my last post. So, I figured I'll just try again and - world of wonders - this time there was no issue with my power extension cable on the card. And NYGM doesn't crash now anymore either. I really fet it were the drivers, just didn't want to go through the hassle of figuring out why newer ones would have trouble with the card. Turns out now they don't, so everything's fine.
Sometimes I believe my PC has a life of its own. Just joking. I *know* it has.