Headphones and keyboard not recognised

Hi,
I have a problem with my pc not recognising USB keyboards and 3.5mm headphones. It's weird because it recognises other USB devices such as my speakers and memory sticks, but when I plug a keyboard into the same USB it doesn't even acknowledge it. I've been forced to use a clunky old ps2 keyboard that it will recognise and box up my shiny USB one!

The problem with headphones is equally baffling (to me). I bought a headset and it worked on and off (both mic and headphones) and now only the mic works, and that's only some of the time. I also tried other 3.5 headphones and it doesn't acknowledge them either. I've looked at where the 3.5 ports for the mic and the headphones are supposedly mapped to and tried every one of them to no avail. I'm pretty bad at all this sort of stuff so could someone please tell me how to change the ports being used to the ones I specify and in a way that my pc will actually acknowledge when they're plugged in?

Thanks.