For the last many months, we've been looking into reports of Dell Optiplex 755 computers spontaneously rebooting. The reboots are random, and we've never found a way to force the behavior on demand. In parallel we've had another issue of the 755s hanging on login with a specific image. The image is hardware independent, and only hangs (although not reproducibly) on the 755s.
Because of the reproducibility issue, its been a long road to troubleshoot. We have a test network, and the problems have not manifested there. What we've found is,
- For the computer hangs on login we've discovered the problem vanishes if the Intel disk controller is configured from AHCI to 'Legacy IDE'
- If we disconnect the DVD drive with the controller in AHCI mode the issue vanishes
So, degrading the controller to 'Legacy IDE' seemed to be good resolution/workaround at least for the hanging issue, so we were going to proceed by...