My CRT monitor goes black (partially) for 5-10 seconds, 3-4 times a day. See the image. This isn't my monitor, but I have the same problem. Only 25% of the screen works and there are 2 very bright lines that separate the black portion from the visible portion. What could be wrong?
Check the monitor cable, probably a bent pin or bad connection, the only other thing it might be is the graphics crd moving slightly? CRT monitor? Didn't know anyone still had them! Edit .. Having looked at the image larger it looks like your CRT may be on the blink, think they use tubes of light instead of individual leds / membraines as do most flat screens so when they fail the whole monitor is useless instead of just a couple of pixels.
Yep, pretty much this. Once a CRT starts to go, it would be more expensive to get it fixed (if it is hardware failure) than to simply replace it with a new LCD.