I had the same problem with my logitech keyboard on the same model computer as you. What I did was press the F-Lock key located on the upper left hand side of my keyboard and then re-booted.
I would imagine to start with that your keyboard is not truly capable of being a usb keyboard, just because you have a convertor doesnt mean it will work as the keyboard still requires the hardware to tell the pc what it is.
So unless you are sure that the keyboard works with a convertor on another pc then you will need to purchase another usb keyboard.
Drivers are not required for keyboards to work at the bios level, however there is sometimes an option in the bios to enable legacy usb mode (but this mode is normally on motherboards that have both ps2 and usb connections).