I had a similar mystery, except it was like every 5th or 6th cube and only happened in the winter. Turned out there were floor mounted heating ducts, and certain cubes were placed just right so that the hot air went directly into the PSU.

Some combo of heat, dust, and static caused gunk to accumulate in the fans, and eventually either the PSU or video card would overheat. The escalation usually came in that the monitor was tinted blue or pink.