PC help-Computer overheating?

Hello all,
I'm having some trouble starting up my Dell desktop. A couple seconds after turning it on, the CPU fan starts spinning really high (fast). The computer will not even enter the BIOS screen and I noticed that the power button is illuminated orange instead of the usual green. I read somewhere online that it might be the thermal grease so I changed that and still have the same problem. I also tried switching out the heat sink and still nothing. The only other possibility I can think of is the motherboard is no good. Please help. Thanks in advance

are their any beeps at startup? did you recently replace the CPU?

The CPU is the original one that came with the computer. I dont hear any beeps at startup either

Try unplugging the computer from the power outlet and push all the buttons on the computer while the Power Supply Unit is in the on position draining all the electricity that still may be in the computer. Then reconnect it and turn the power supply on after you have switched the PSU to the off position just before re-pugging it into the outlet.