You've run for four hours - no problem - or many crashes in 30 minutes - whats different?
Two more thoughts.

Direct X also does stuff with audio and other media on the PC. Could this be related to your sound or music processes? Are all those drivers current?

Finally, it could be unrelated to direct X. I had an issue where my PC was "randomly" rebooting. Turns out it wasn't random - it happened a few minutes every time I plugged my phone into my PC. Of course I plugged it in every time I sat down to play and was blaming all kinds of things for a while..

Good luck.