When you connected the PS/2 keyboard I'm assuming the USB one was disconnected.
Try a PS/2 and just hit the Del key and keep hitting it.
If your pausing on post BIOS then it's trying to resolve what to boot off.
With the PS/2 keyboard when it gets to this stage does the caps lock light on the keyboard work?
(Like if you hit caps lock does the light on the keyboard light up)
Do you hear any "ticking" coming from inside the case?
Also for now I'd unplug ANY external devices baring mouse, keyboard and screen from the computer.
Lets see if we can at least get it to get past this.