Just wanted to provide an update. Upon further inspection, I found there were bulging capacitor between the two rows of memory slots.  There's a total of six of them.  Almost all of them were bulged on the top, some of the oozing yellow electrolyte outside.  Replacing those capacitor seemed to addressed the issue.  I am now able to boot into Windows & Ubuntu perfectly fine.  The CPU temperatures were never beyond ~50c even under stress test. Before the repair, I am also getting the "CPU 0 : General Protection Exception Occurred." error as detailed in this link: [URL] Although switching to version A08 BIOS resolved the error, it was never able to get through the Windows or Ubuntu boot. I hope the journey I took can be helpful to folks having same issue in the future.
I have a Dell T3400, with Intel Xeon x3360, no overclock or anything.  It recently developed this issue of thermal shutdown during the boot process of Windows 10 or Ubuntu. The machine basically turn itself off during the boot process. Then on the following boot, the BIOS displays an error message stating that computer was shutdown last time due to a thermal event. The weird thing is, the computer runs fine in DOS.  The BIOS diagnosis (F5 when prompted with an error) which runs for hours perfectly fine without showing any issues or displaying any error. I know this may because they use much less CPU power. But I checked and applied new thermal paste. The CPU heat sink is clean, never hot or even warm to the touch. The fan is clean and never kick in to higher speed either. What other possible cause of the thermal shutdown? What is the best way to diagnose it given that I cannot getting into Windows or Ubuntu...Can you enlighten me from your abundant experience? Thank you very much in advance.Regards.
Dell T3400 Thermal shutdown in Windows 10 & Ubuntu boot, but not in DOS & BIOS