Mac Pro will not start. Constant power light flash.

I have a Mac Pro from 2008, (I believe) that does not want to start up anymore. No signal is sent to the screen for it to start up. The led power light flashes with a constant frequency, app. twice per second. The fans starts as usual. I have tried to rearrange the RAMs, use them in different positions, as well as using only a single one (also tried different RAMs as single). Four red lamps flashes up briefly on each of the RAM boards. I have tried to remove the four 1TB disks one by one, without improvement. I have also replaced the CR2032 lithium battery and pushed the little button in the upper right-hand corner of the board. Same result: fans starts, power lights on and changes to the “permanent” flashing with a constant rhythm. Nothing happens on the screen, no indication of activity in its power light. The only thing I can do is to force the MP to shut down with the power button.

The system is one of the latest published for this computer.

Please, is there anyone out there with a clever idea, other than leaving it at an Apple Store for examination?