[Challenger Ultimate - F, G, H, C, left Start not working]

Hi, I'm having a problem with my recently purchased (as a birthday present) Challenger Ultimate keyboard.

 

The left Windows key and F, G, H, C keys do not work when pressed. I've tried uninstalling and reinstalling the drivers/GUI, resetting the configuration, using different USB ports on the back of my PC - nothing has worked.

 

I'm currently using my old keyboard for the time being.

 

I can't find any information anywhere about keys not working on Google, or this forum, so suspect this may be a one-off defect.

 

If anyone has any ideas, I'd be glad to give it a try.