Hi @random_user_101 ,
What is the make and model number of the desktop computer or if it is a custom build the make and model number of the motherboard?
It may be that the BIOS is corrupted and it can't POST properly.
Disconnect the AC power from the computer and check if there is a button cell battery on the motherboard.
If there is gently remove it (note the orientation so that you replace it the correct way) and then press and hold the computer’s power button for 10 seconds and then release it.
Reinsert the coin cell battery , reconnect and switch on the power and then try to start the computer.
If it starts OK if may be that the battery has been depleted and needs to be replaced.
Be aware that this will restore the BIOS settings to their default value, so if you had any settings tailored for specific hardware/operating requirements you’ll have to go back into BIOS and change them back to what you had
This battery maintains the BIOS settings when the PC is powered off and when it starts to deteriorate the settings could become corrupted.
They usually have a life span of 5-7 years and are not the rechargeable type.