"Abandoned" Xbox One S Revival

Hi everyone!

A while back, I bought an Xbox One S off someone via Facebook and he told me he had removed the hard drive from it and then left it in storage for yonks. I didn’t check to see if it would run without the hard drive but the man told me it would start up and the stop after 20-30 seconds with nothing on the screen. I gave it a good clean, replaced the (perfect amount of) thermal paste, installed a new hard drive and everything seems to be working fine (a disc came out of the optical drive) but got nothing on the screen and it still turns off after 20-30 seconds. Not only that but when I try to press the Sync button, the light doesn’t flash. It makes me wonder whether the power board is broken as well despite being able to start up. Any suggestions/questions?