Question Computer turning on immediately when power supply is plugged in

So I took out the heat sink and CPU and cleaned/wiped it off to rid the dust bunnies and now when I plug my power supply in, the computer automatically turns on and the fans ramp up, and I don’t even get a BIOS menu or anything, with or without a graphics card installed. No matter what I do or what I unplug this action doesn’t change. And the same thing happened with my last OptiPlex I bought. So what am I doing that’s wrong?

This happened with my last computer also. I had it just about or more than 2 years until I cleaned it out, with everything above happening after the fact

My new computer, which arrived a few days ago, that I just cleaned out, has everything happening as described above.

The computer is same make and model, same memory installed, same CPU (but new as it arrived in the mail). The only difference is there is a 1TB hard drive plus a 500GB hard drive instead of 2x500GB.