If you only see white led on power button it is supposed to mean pc is normal.  Check video cable connection to both pc and monitor, try a different cable and different monitor or confirm both cable/monitor do work using another video source.
When I plug in the power adapter I get the white led for about 12 seconds and then it turns off for about 3 seconds and then comes back on for about 12 seconds and then goes back out etc. With the cover on I don't get any amber lights that I can see. When I take the cover off and look at the led I can see that I am getting amber lights. I can't see the amber lights if the cover on.   The pattern is power on white led 12-14 seconds, led off for about 3 seconds, white led on for about 12-14 seconds, led off 3 seconds, Amber led blinks on then goes out for about 10 seconds then blinks on again and off. The pattern then repeats.  I think this means the cpu is bad but not sure. Any suggestions? 
Optiplex Micro 5090 won't boot