MAcBook Air wont start up propery

Hi,

I'm having a problem starting up my MacBook Air.

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.

Can you help me pleeeeeeeeeease