After replacing optical and HDD drives computer will not boot/chime.

I have a E2374 iMac. The optical drive died years ago, and the hard drive recently failed. I have an SD card boot disk that I used to run the computer multiple times trying to recover some daily files on the machine, but it's toast. Won't even start up in target disk mode with the internal drive.

I decided to go ahead and swap out the optical drive with a Samsung Eco 850 SSD and used a WD green 2 TB hard drive I had laying around. Followed the E2374 guide and everything went mostly smooth. After putting it back together there is no action from the machine when pressing the power button. Tried multiple power sources (but only have the one cord).

The issues I (may have) had with the install were:

1 - The thermal sensor and tape that cover it on the optical drive obviously didn't seal down as well as before, but both stuck well and stayed during installation. (Not sure how this would affect its ability to power on though)

2 - The hard drive I was replacing was a Seagate 1 TB and like I said I put in a Western Digital 2 TB I had lying around. There were 3 connectors into the Seagate one connection of which (the guide called it thermal sensor cable) was not on the Western Digital. I read something after googling for a long while that you could just put that cable's connectors to the top 2 pins of the jumper pins on the WD drive. I bent the pins down slightly like the comment said and stuck the thermal sensor cable connector in there. Closed her up, and got nothing.

I don't understand how connecting the thermal sensor cable in that way could stop the computer from at least booting up, so I guess I'm concerned I may have damaged some discreet power supplying cable in some way. I believe I was gentle enough to not have caused any damage, but this was the first time I've ever opened an iMac.

My next step is to remove the HDD completely and see where that puts me, but it's too late tonight and I don't hold much hope.

Thanks in advance for any advice or suggestions.