So, I switch an i7 7700 to an i7 8700k and when I tried powering the pc it didn't give any signs of life. I reseted the CMOS , then I took off the battery and put it back on , tried to reinstall it multiple times w new paste and each time no sign of power nowhere in the pc
Asus prebuilts are some of the best non-botique gaming PCs.
That said, the socket may fit but the chipset might not. Intel has been on LGA 1151 as the socket size for the past 4 generations of Core CPUs (6, 7, 8 and 9). However changes in the pinout has made it so CPUs support has changes. Basically it was this:
100 and 200 ran the 6 and 7th gen
300 runs the 8th and 9th gen CPUs with a newer one for high end 9th gen the 390 series.
So most likely you have inserted a CPU into the board that is not supported. You might want to try the 7700K and hope your board is not dead.