Usually I don't shut down my MBA but I shut it down recently and now that I have turned it back on it stalls and only shows the grey screen with the apple logo and the swirling 'loading' symbol and it doesn't change from this screen however long I leave it.
Also, when I do turn it on I dont hear the start up chime.
Good chance that you are suffering from the freeze/kernel panic plague. Zap your PRAM and retry. If it doesn't help do a system reinstall. If that doesn't help it's refund time: the official stance from Apple is that there is an issue, they do not know what it is, and there is no ETA for a fix.