No signal from Displayport, only from VGA Optiplex 7010

319-0914 : 3rd Gen Intel Core i5-3570 Pro cessor (6MB, 3.4GHz) w/HD2500 Graphics, Dell Optiplex 7010

No aditional video card, just de embeded intel hd2500.

The problem is, that Im trying to use the Display port instead of standard VGA cable, but, If I connec the display port to my monitor (display port input) no signal is detected in my monitor. I have tried the two different display ports on my dell, but no signal is detected on my monitor, so I need to use vga port.

I have this problem with two different optiplex 7010 that i own, one with windows 7, and the other one with windows 10.

I run the self diagnostics, but no problem is detected.

I appreciate your help.

Thanks