K11 air con problem?

My air con has stopped working or should i say the light on the dash has stopped lighting up when pressed, also no drop in engine rpm either.
I had it regassed Jan last year and was fine but now when you press the button nothing happens.
I have checked the internal fuse and thats ok.
What else should i be checking?
Many thanks rct
Pressure may have dropped in the coolant. If there is not sufficient pressure, the Air-con will not come on. I've used the DIY re-pressure system (Ebay) and it works OK but, of course if there's a leak (most likely in the condenser in front of the Rad) then a re-pressure won't help. The DIY system comes with a pressure gauge that lets you check.

Alternately, the air-con relay may have failed. It's above the fuses in the drivers foot-well.