Broken Dell Optiplex 9020

Recently I bought a Dell Optiplex 9020 that I planned to eventually turn into a gaming pc. My first step towards completing this task was to install a new cpu. I was trying to install a i7 8700t that I had laying around but I came to the conclusion that the 8700t wouldn’t fit in my Dell Optiplex. So I took out the 8700t and put the i7 4790s that the optiplex came with back in. Since putting the 4790s back in the power button is amber and the optiplex won’t work. Any advice?