GX270 go up, GX270 go down

The Dell Optiplex GX270 that I use for a Fedora test platform and number crunching station has been behaving badly lately.
Symptoms: Abrupt system shutdown characterized by the screen going blank and a brief whir from the CD drive. System completely unresponsive, although power light remains on. Completely dead. System must be powered off to be restarted. Attempting to install FC5T1 reproduces the shutdown pretty reliably. Otherwise the shutdowns occur intermittenly.
History: CPU fan failed a couple of months ago and was replaced, with problems starting shortly thereafter.
Diagnosis: Suspect the cause is heat related hardware related. Shutdown is abrupt, with no messages logged by the OS. Perhaps there was some thermal damage to the CPU when the fan died. Consistent shutdowns during software installation attempts further suggest heat related hardware failure, with increased heat build-up from CD drive contributing to the problem..
Treatment: May have to resort to calling the Helpdesk to see if I can get a replacement system.