The Desktop does not turn on. When switching on the front power light lights up and remains lit - with no flashing.

The fans turn for one second then stop and the rear power light switches off. The display is always black.

I have followed through the various steps on the product support page, and the virtual agent, including removing all external devices connected to the PC and retesting, then checking cables, changing the power cable, resetting the CMOS battery and checking memory cards. 

Does anyone have any further advice on what the issue could be?

thanks in advance for your help.