LattePanda 3 Delta does not power on

I had not used the LattePanda for several months, and recently when I tried to turn the PC on, it would not power on. The symptoms are as follows:

1. The power LED does not turn on.

2. When the adapter or a PD charger is connected and the voltage at the DC connector is measured, 14V is present.

3. When measuring the 5V at the USB pin header, 5V is present.

4. When measuring the 5V and 3.3V at the BIOS pin header, the voltages are present.

Could you tell me what might be causing the power not to turn on?