Vostro 220s won't start up

I have been on holidays for several weeks and my computer has been switched off. I turned it on and got a blue screen which recommended I turn it off and try again. I did this and while power is going through to the computer, nothing appears on the screen. I push the button to wake up the computer and it gives message "no signal coming from your computer..." I have pressed buttons on the keyboard and the mouse but nothing happens. I have unplugged it at the wall power supply and tried again, still nothing. Has anyone got any ideas?