Computer boots when powered on but after a second it reboots

[MaatB]

When I push the power 'on' button on my computer it starts to boot. But after one second the computer seems to shut down. The power light turns off, the fan stops spinning, internal lights turns off also.  After that the computer boots again automatically and succesfully Windows 10. There are no messages whatsoever on my screen. And no error beeps.
This issue also happens when there are no usb devices connected. When  I have connected my external usb harddisk it will start en stops, en then start again during a boot. I don't think that is healthy for my external HD.

[Hibb1]

This usually happens after a BIOS update, or when resetting the security settings or enabling virtualisation.

Try going into BIOS and loading setup defaults, then loading/resetting security & TPM defaults. This shouldn't affect your boot drive unless you have BitLocker enabled. If you do, only do the setup defaults.

[MaatB]

Thank you for your reply! Unfortunately it didn't solve the probem. I followed your instructions in the right order you proposed. Loading setup defaults and resetting TPM defaults.