My asus screen wont get any singal

hey guys, i bought my new asus desktop a month ago and on the keyboard there is a quarter moon key , i wondered what it did so i pressed it .. then the computer went to sleep .. so obvious so i turned it back on and the screen is getting no single ... but everything else is working, i replugged all the cords and it's still not working.... someone help me please!
the desktp is : windows 7 professional , 4gm ram , 1.5 tb hard drive , 2,76 ghz