I currently have the motherboard of a Dell XPS 8930 in a Thermaltake CTE T500 case with a Corsair CX750M power supply.

The machine complains about a defective power switch cable on boot, because the Thermaltake's power button does not have the special Dell magic - but it had been running fine like that for months.

Recently, however, the machine has been rebooting once or twice a day, most of the time when I am not around - either in the middle of the night, or while I am at work.

I was in front of it once when it happened: The screen turned black for a moment, then the machine booted up. It was as though someone had pressed the reset button. The reset button, by the way is not connected, but the cable is tied away safely, and can definitely not touch any metal parts.

This started right after my UPS died; I had the PC plugged into the wall for a while, and that was when it happened first. It is now plugged into a UPS again, but that did not make a difference.

This far, I've verified that all connectors are firmly seated (including RAM and the video card) and reinstalled the OS. I've visually inspected the motherboard - no bulging capacitors or similarly scary stuff as far as I can tell.

I guess the next step would be to replace the power supply. It is quite new, but I suppose it could have gotten damaged, or just be a lemon.

Any cool ideas for other things I could try before I do this?

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The power supply on my XPS 8930 gave up the ghost, so I replaced it with a Corsair CX750M (probably not relevant).

While I was at it, I also replaced the case with a Thermaltake CTE T500 (probably relevant).

I connected the power switch to pins 6 and 8 on the front panel connector, following the diagram at XPS 8930, GPU and CPU Liquid Cooler, PSU, Case Swap, Upgrade.

Things work as expected: I can power the computer on and off with the power button, all cool.

BUT: Every time the computer boots, I get an error message from SupportAssist during POST: "[...] Alert! Power Button Cable failure". I click Continue, and everything is peachy.

Does anyone know how I can get rid of this message? Did the power button in the original case know some secret handshake that the new one doesn't?

At this point, I would be OK with disabling the SupportAssist self check altogether. I don't need any SupportAssistance to know that the machine is getting a little cranky.