PC won't start after adding a new hard drive.

[northernwnds]

I recently built a new computer from scratch and got it running fine. After just a little bit of troubleshooting, it posted and I was able to install Windows and everything ran smoothly. I tried to add a secondary HDD after installing Windows on an SSD, and now the computer won't turn on at all. I double checked all my cables as best I could, and i can't see anything that isn't plugged in correctly. I will list the specs below. Any ideas?

i5 8600k
16GB ddr4 2666 ram
gigabyte z37op d3 Mobo
Nvidia GTX 1080
Corsair CX600M PSU
crucial 250gb SSD

Thanks in advance.

EDIT: forgot to mention, even if I uninstall the HDD the PC won't start at all. No post or power.

 

[hang-the-9]

Have a second person that knows how to build computers look over the system. We can't see if anything was unplugged or is in the wrong spot.

 

[stdragon]

Check your case power button wire. It's possible you knocked it loose while working inside the computer. Also check that no other power cables came loose as well - both to the motherboard and PSU if they have modular cables too.