Only boots when power button is held down; strange behavior
Any suggestions you have would be greatly appreciated! Here's the situation:
I just got my hands on a 2012 Macbook Pro 15". I got it pretty cheap because the seller said the computer wouldn't get past the grey screen or Apple logo when booting. I figured it was likely an issue with the hard drive and bought it anyway. Sure enough, when I put my own hard drive in there, the computer doesn't get stuck on the boot screen.
HOWEVER, it will only turn on if I hold the power button down until I hear the click/whirr of the CD drive. If I just press the button, the SIL will turn on once and then nothing. I don't think there are any mechanical noises when this happens.
Once on, the computer appears to work fine. It's a little sluggish to boot and to respond to inputs, but that could be because of the 8 year-old HDD running High Sierra (just as a tester), or because the OS was installed on an entirely different machine (2010 13" MBP, 2.4 GHz C2D).
Thanks for your input!
I've reset the PRAM/NVRAM and tried resetting the SMC, but I couldn't tell if anything happened.