Nissan Micra Heating not Blowing on Drivers Side?

Hi, I'm hoping someone can help!

I have a 1997 nissan micra which has a glitch with it's heating. It was working fine last night but I switched it on this morning and although the fan works fine it's only blowing hot air (noisily) on the passenger side, nothing on the drivers side at all.

I'm wondering if it's a pipe or something that's come lose, but have no idea where to start to look for the problem or what you nice people might think it is?

Any help appreciated - greatly!!

Thanks :-)