cannot restart computer and will only shut down

[westom]

Is there anything there that would cause this?

You problem is within the power supply controller (probably). There are a number of reasons for this. About half require a multimeter to see what actually exists.

The front panel switch could be wired incorrectly so that is works sometimes - not others.

Voltage levels on signals from and to the power supply controller must be measured for sufficient margins. In fact, that 30 seconds of labor would have been the very first numbers I would have collected.

Also if a wrong HAL is installed by Windows for your hardware, that also can cause problems. This is what others also described as incorrect ACPI software. A multimeter may also identify symptoms traceable to that problem.

The ability to restart a machine is in a power controller - hardware on the motherboard that interfaces with the ACPI. That hardware is unique for each chipset manufacturer which is why Windows must load the correct software. Unfortunately, then is no manual selection and reload process (except if the motherboard manufacturer has one).