20w 16MR downlighters?

I have just had a bulb stop working I assumed it was dead, but when I replaced and put it back ito the flush downlight casing it did not work. I took it out and refitted it but this time left it hanging on the twin flex it came on but every time I fit it back in it goes off again. I can't work it out and can't get in too far to see any cable problem - it does not make sense it has worked for years and now will not work - any ideas i.e. could it be the two pin connection?