MBP won't power on unless I remove the hard drive

I bought a macbook pro a1286 2010 model and was told it was probably a DC jack issue that caused the computer to not power on.

Just being curious I plugged it in and turned it on, and it worked just fine.

Then I installed a new hard drive and now it won't turn on.

So I replaced the DC jack, still it won't turn on

So I took the hard drive out, and it turns on fine.

That being said, I can't turn the computer off by simply holding down the power button. I have to unplug it for it to turn off

I've installed a new SATA cable to see if that was the issue, and still the computer only powers on without a hard drive installed.

What could be the issue here?