I turn my computer off and everythin was fine. Now I turn it on again and red seems to have disappeared. Evrytime there is something red on the screen it goes black or grey, and in Word, Excel etc there is no option to select red from the colour palette???
sounds liks your monitor has gone bad. Sometimes the red projection part of the monitor can die out, and sometimes it can be a broken wire or connector. If it's just the cable, that's pretty easy to fix, (especially if the cable screws on at both ends!) however, if you don't want to/aren't comfortable with splicing the wire, or it's the internal part, you may just have to get a new monitor. Of course, if it's new, check the warranty.
It's either your monitor or your video card/drivers. Check for upgraded drivers. There could possibly be a conflict somewhere.