Dell optiplex 755 wont boot

[HTOOOS]

Hello,
I have a Dell Optiplex 755 - have had it for about 3 years and it isn't booting at all. It is getting power ( power light is green) ~ but it won't even give me a message as to why it isn't booting. Suggestions?

 

[Ubrales]

Do you have a USB or external hard disk plugged into the front USB port?

Just remove it and start the computer.