My little sister has a 4 yr old desktop with an old acer CRT monitor. It worked fine in the past years, then a couple of months ago the monitor menu suddenly pops out for like an hour or so which you can't exit (and even in the rare cases that we could it still pops out again a split second later), which makes reading a hassle because the menu pops in the middle on top of every program. I searched google and a lot of people are having the same problems but there's no solution. Could anybody help us? 
Thanks!

Sorry I can't help you, but I know it would help others that may be able to help you if you were to provide the brand/model of the monitor.

I had a Sony Trinitron die because the menu system got really fucked up.  Started displaying text in all sorts of languages and generally killed the monitor, I was able to get a replacement of the same exact model, but now even that CRT has yellowed and I'm regretfully on LCD (albeit the best LCD monitor you can get).
 
Basically if the menu system is messed up, IMO the monitor is in bad shape, probably not fixable at a reasonable cost.

Toss it and get a new monitor.  It's not worth it taking it to a shop, and trying to fix it yourself will likely get yourself killed as the capacitor in them holds one hell of a charge.  Just toss it dude.

Toss it and buy an inexpensive LCD.

Toss it and buy a 22" or 24" monitor. It's cheaper these days and trust me, you won't ever go back to crt and the lcd monitor will last 10 years before it breaks down, you are saving money. Just don't get too small of a lcd monitor like a 19" lcd monitor, it's rectangle of course, you will have less screen that way.
 
I also think once you use a lcd monitor, you won't go back to crt ever.

Yeah get an LCD its also better for youre eyes and color are so much better :D

" Yeah get an LCD its also better for youre eyes and color are so much better :D "

" Yeah get an LCD its also better for youre eyes and color are so much better :D "

just the power usage alone is reason to get rid of those old crts