Hi @proelectronics ,
Test the PSU using the paperclip test to check if all the voltage outputs are OK.
Has this PSU worked OK before in the desktop or is it a replacement for the original?
If the PSU tests OK, according to this link, a blinking amber problem with this particular PC model is in the front panel which houses the USB ports and the Power On switch.
Some have solved the problem by disconnecting the panel from the motherboard, which makes it hard to start the PC as you have to know which pins to short out, simulating the power button, to start the PC.
Others say that by just disconnecting the wiring from the USB ports in the panel itself (damaged pins apparently) resolved the problem.
Here’s an image taken from p.67 of the owner manual showing the location of the front panel header pin connector, that may help.
(click on image to enlarge for better viewing)