Need help, something is wrong with my LCD monitor.

Hi, lately I have been having problems with my LCD monitor, it has darker and lighter horizontal lined "strobbing" on an off all the time, today it was doing that almost the entire time for almost 9 hours, in the past it also happened, but this was usually gone after 5 or 10 minutes so i did not care much about it, but now it is unbearable, and on top of that it seems that whatever brightness, and contrast settings I set it to it makes the monitor bright all the time(to the point that i have to squinch my eyes a bit because its too bright... I had it always set to a much darker, contrasted view), is the monitor dying on me? I had the monitor since around mid 2001, or is this related to some other issue? I checked the cables, and they are ok(the same ones I always used)the plugs were all connected, the only thing that I changed was the gpu(to a 2900xt) 2 weeks ago,but i had these issues prior to the upgrade, so i dont think its related.

Thank You for all opinions.

I can not this is the only system that i have, I did buy a new psu with the gpu, the one that im using right now is a thermaltake though power 700W, and i have to admit that i think something is a bit wrong with it, since day one it was getting quite hot(compared to my old 480W psu), but i guess the power consumption increased as well, so that might be a reazon for it, but i still think its getting a bit too hot for what it should be.

I used a different psu before(thermaltake 480W purepower) and i did have simmlar issues once a month or once per 2 months or so, so i was thinking it was the monitor, since about a year ago i exchanged all my motherboard, cpu, ram, and gpu, and i had these issues even prior to that.
So i figured that this might be a the lcd issue.
Actually this stopped about 40 minutes ago...quite odd, since i did not do anything. But the screan is still a bit too bright compared to before (even with lower brightness settings than before)
btw just out of curiosity i have noticed that the psu has a plastick (made probably out of isolation tape) "plate" right in th eback of the psu, and it blocks a good half of the exhausted air, so half of th eexhaust is really hot, the other one is i would say room temperature, i was thinking about removing that plastick but it would be very hard to do it threw those tiny exhaust (comb like)

I think your LCD monitor is finally dying on you. More specifically, it's probably the circuit board itself that controls the monitor is going bad.

Try to take it round a friend's house or borrow someone's laptop to try the monitor on.

I'm guessing it's the LCD that is the problem here as well and as suggested above - trying it on a different system would confirm the issue.

Thank You for all the information, much apprecieated, actually the flickering has stopped, and the colors did come back to norm, so i guess all is ok, but i guess it might happen again.
In regards to testing out the monitor somehwere else, it is rather inpossible.