Mac Pro 09 won't turn on display, fans work, red light on memory tray

My 2009 Mac Pro A1289 won’t boot up. no display but I can hear the fans loud.

As soon as I turn on the computer, this red light next to the RAM comes up (1st picture)

so, nothing happens for a long time… then I press the power button to turn it off and the other red light under the 1st Hard drive slot comes on. (2nd picture)

…With the computer on, I pressed the TEST button and you can see the PSU led on green (I assume its good) and the 5V STBY in yellow (3rd picture)

I have no clue about anything… please heeeeeeeelllllp