I didn't yet read that part where you said it.
Disconnect the PSU, press the power button to remove any remaining Electronic Static Discharge (ESD) inside the case.
When you go inside the case and touch something when there is ESD present, you may damage a component.Open the case, discharge yourself too before going inside!
A little car shock you sometimes might feel divided by 10 is the max power a component can handle.
Search for the cmos battery, pull it up for a second and put it back.
The cmos battery looks like