My PC doesn't start

[jack armand]

Hello everybody I have dell optiplex 755 that does not start .the mouse is noth working neither monitor .keybord. just two numberes on (have green light) 1and 3 .and 6 long bip and it s quit again and still in power til I take the cable off or pressing the power button.
I am verrry thankfull for considerring helping me.

 

[Tmagic650]

Your computers memory has failed... Try swapping the memory sticks first. This could also be a motherboard issue