MacBook won't boot past grey screen.

After turning off my computer yesterday to give a quick wipe over (dry cloth) I tried to turn on about an hour later, and it wont't turn on past the grey screen with apple and spinning cog, it just turns off.

I have tried restarting it several times and same problem, I have also tried restarting in safe mode, resetting the smc and pram, and after all this it is still doing the same.

Please help! I've tried ringing apple but they have said my apple. Are protection is out of date so it's £35 just to talk to someone!