|First, has the color been adjusted since the last time it worked correctly, using the monitor's OSD or other means? Did anyone open the back of the monitor and fiddle with any of the potentiometers? You know, those small metal cans on the circuit board that invite a screwdriver blade? If yes, then take the monitor to a repair shop. If no, then continue:|
1) Loose or bad PC-to-monitor cable
2) Bad red electron gun in CRT monitor
3) Bad video card
Swap it temporarily with a known good monitor. If that monitor works then it's not # 3.
Swap the red-less monitor back. Check that its cable is tightly connected. Wiggle the cable where it goes into the monitor and where it connects to the video card adapter. If you get no flashes of red then the cable is probably good. In that case the red gun is bad and you may as well toss out the monitor and get a new (or less old) one.
Now that's what I call a sticky situation