It's completely my fault!

I think I killed my computer and it's totally my fault.
Nothing turns on. Well, there is a little green light on my mother board but other than that there are no signs of life.
I had several old harddrives that I wanted to transfer to a SSD. I had the cover off and was connecting/copying them one at a time. On the 2nd one I connected it without powering down my computer and I apparently shorted something out.
Is there anyway to reset it or is this going to be an expensive lesson or both?

Please help if you can!

It's hard to know what shorted out. If the motherboard got damaged, there's no way to "reset" that.

Definitely disconnect the drive you connected when it shorted out.

If you have a spare PSU, you could try that. It's possible that something shorted in the PSU when you connected the drive.

For file transfers, it would have been safer to have a USB to SATA adapter or enclosure. Make sure to get a "powered" adapter for use with 3.5" HDs. Something like this:
https://www.amazon.com/SATA-Drive-Ad...s%2C218&sr=1-3