why does my macbook air turn on then shut down?

I was trying to clean my computer and download word but then my MacBook air froze and I manually had to shut it down but now every time I press the power button it turns on and loads for 5 seconds then shuts down again. I left it charging for a day and tried again but its still not working, I literally have tired everything. HELP ME :/ 2011 MacBook air.