Black Screen On Startup

I have a Packard Bell Easynote ARC21.

My brother, who thinks he is a computer genius, changed my bios/cmos settings (you know, the ones where you press an 'F' key on startup.). He changed the settings for what i presume were graphic card overclocking and something about 10% voltage or something along those lines.

The computer was rebooted and now all i get is a black screen, as in, the monitor does not switch on at boot. the lights for HD lights on aswell as the power light and i can hear the fan spinning and the HD whirrs for a bit.

I have read a few forums and havent seen anything like a problem the same as mine. I tried to reset the CMOS by taking out the watch-type battery and then replacing it as some forums have suggested hoping that this would solve the problem. No it didnt. Still the blank screen.

This is really pickling my head so please help me. Any advice at all will be fully appreciated. thanks.