No joy after upgrading

My hard drive went out . So I got the bright idea to swap it out. While I had it out I decided to swap out the i5 processor with an i9. I have done many many many pc upgrades no problem. But alas my iMac has said no. Now with putting it all back together only the 2nd light of the 5 leds comes on and stays on when plugged in. I have taken everything back out and ensured it is all plugged back in accurately. Why would the first light not light up? Also nothing seams to happen when pressing the power button.