Dell keyboard Model RT7D20 PS2

I have this old Dell Keyboard with PS2 connections, I have just got a PC but it does not have PS2 connections on it only USB, I have bought an adaptor that converts PS2 to USB, but my PC does not recognise the keyboard, I need to know if this keyboard is USB compatable, if so how can I get it to work, do I need any drivers?

I have seen one for sale on ebay, and they provide it with an adaptor, so I assumed it was USB compatable.

Thank You Paddy