Onto my second brew, first one is bottled and just waiting to be drunk

Now, Just put down a IPA and after 48 hours I have no airlock activity - I also had zero airlock activity with the first brew.
However, with the first brew the yeast was quite obviously doing it's thing and I so I thought I had a dodgy airlock/gromet. So I went to the local HBS and got a new gromet and airlock for my second brew - However I still have the same result, no airlock activity but the SG is dropping and looking at the brew, there is definately something going on.
The only thing I can think of is my lid is bung? Would this just be the "o" ring? as I would assume that is what makes the seal?
Where can a new "O" ring be purchased from? Or should I just move onto my 75L fermenter?

I just get frustrated reading about everyone's airlock bubbling away, when mine does sweet f--- all.......

Cheers
Mick