Facebook Marketplace Xbox One X dud (turns on for a second or 2)

Bought an Xbox One X on Facebook Marketplace under the impression it was “totally fine”. Of course I brought it home, it didn’t work, and the seller blocked me on Facebook.

Anyways, I’m trying to fix it now. The light turns on and it dings, then the light turns off a second or so later. I took it apart completely, making sure everything was plugged in securely (and reapplied thermal paste while I was in there), but no luck. Still the same problem as of right now. I’ve seen some posts with similar power failure suggesting it is the APU. I’m assuming that would mean an entire board swap which would be probably more expensive than the $150 CAD I paid for it.

Any chance it would be something simple like the power supply? Does anyone have suggestions for mail in services in Canada (trying to avoid international shipping fees)?

Thank you for any help!!