Dell Dimension 2400 Won't boot

Greetings,I have a Dell Dimension 2400 will not boot pass the Dell logo. I have tried so many things but what I noticed is that the computer will only boot if I plug in another keyboard in the Ps/2 port it will boot as normal and I can use the USB keyboard plugged in so basically the comouter wants to boot with a keyboard in the PS/2 port.

The diagnostics lights at the back of the computer A=Green B=Orange C=Orange D=Green Dell does not have support for those colours!