Computer screen help????

Ok I run a windows xp and I turned off my comp and left 15 mins later my screen is all weird. The colors are diffrent and games don't work like I was in safe mode or something. I get this thing that says something like the depth of screen is really low or something and to press the ballon to fix it and it did nothing. I dont know what it is the only thing I downloaded was the msn messager. Plz help me.