A PC based on the DH55TC Desktop board is intermittently failing to start properly - at power-up, several beeps are heard, then a spontaneous reboot, then a BIOS screen showing Processor Thermal Trip (escape to proceed.) This happens ~10% of the time the machine is started.
I am certain the machine is not overheating (CPU temperature is monitored with a software application, and in any operating mode is well within normal bounds). The machine does not crash, halt or have other problems during operation, only at start-up. The problem also seems to appear only at power-up (rather than reboot.) Usage is typical office productivity applications (nothing that would stress the CPU.)
The CPU cooler was (carefully) replaced - the old one used thermal compound (thoroughly cleaned from CPU surface upon removal); the newer one has several strips of thermal material pre-attached to the heatsink contact surface. Again - there is no circumstance where the CPU can be made to approach thermal limit during operation; the processor thermal trip message is occurring at *cold* power-up only.
The PC internals have been (carefully) cleaned of dust.
There have been no recent changes to the (air flow) sounds the PC makes.
BIOS was updated from Version 38 to Version 48 without correcting the problem.
The PC internals and surfaces have been (carefully) cleaned of dust.
All fans (front and rear case fan as well as CPU cooler fan) rotate normally and are unobstructed.
The power supply appears to be operating normally with no unusual internal fan noises or other sounds.
The PC case includes a vent duct from a side panel towards the CPU cooler; this is in place.
The problem is fairly new - the machine has been in daily use since new (~2009 timeframe), and these warnings began appearing about two months ago. The remedies above have been tried to no avail.
I searched communities.intel.com for mention of processor thermal trip warnings - there appear to have been some other types of machines during the same era that experienced unexpected processor thermal trip warnings, but I didn't see anything specific to DH55TC.
I wish to avoid replacing the machine and being forced to Windows 10 (I would like to remain with Windows 7 and the machine is otherwise serving it's job well.)
Recommendations how to proceed?