Sounds like your tube is on the fritz--time to get a new monitor. Could be your video card--have you been able to test it the monitor on another computer?
- Color? (Deep orange, kind of faded, light rainbow)
- Organized? (straight lines, constant width/size)?
- Disorganized? (random dots, segments, waves)?
- Traveling? (moving from where to where)?
If it's a light rainbow, it could be a magnetic field from an electronic device deflecting electrons from the cathode ray gun (unshielded speakers commonly cause this). However, there needs to be a dynamic magnetic field for this to occur intermittently, i.e., speaker power needs to be changing or speakers need to be moving.
I have a Samsung flatCRT monitor and occasionally I'll see orange lines going across the right side of the monitor. After about 15 seconds all the lines disappear. What's going on here? Thanks!