Don't really think it's heat or it wouldn't capture to the other drive either. For some reason, something starts hitting the C drive so hard that it's on solid. I haven't yet figured out what it is.

Performance tweaks
 

If this is a windows system, try turning off the indexing service, which is pretty useless anyway (just organize your files logically and you won't need that service stealing CPU cycels). Also consider a defrag occasionally. Lots of video editing can trash a system (though not as bad as a year of surfing the web with a large cache enabled... all those little cookie files getting fragmented). I'm just throwing out random suggestions here because that is quite an odd problem.

jason

Indexing is off. It has been defragged on occasion and, I think, I did it after it happened once and it happened again afterwards. I can live with it as I can capture to the D drive and then copy some of them to the C drive if needed. Curiosity really wants me to find the cause, though.

Curiosity
 

Same here, especially since this is the kind of problem I might encounter in my home computer consulting business (one way to make ends meet at least). It has me stumped. You have already tried the solutions I would have tried. Have you considered a witch doctor? Or may be the computer needs a bribe... some fancy new device to attach to it and make it feel all special. :-)

jason