As a last resort, I'd suggest the old approach of ruling out things one at a time. Make a total re-install of FSX - a complete wipe from your HDD, the LOT of it. Then install your addons one at a time, followed by a test flight after each addon. When you experience this problem again, you may well have your culprit. Again, this would be the last resort.

I have to agree with Matthew. When all obvious trouble shooting brings no results, for what ever reason, FSX some times needs a spring clean. I have always made a point of putting all my FSX a/c and add ons load information on some disks and or mem sticks so I can get to the reload keys, reload sites, disks etc without too much drama. When FSX is driving you crazy with "issues", I wipe the drive and reload.Still takes a few days,but always amazes me how much better FSX is.

Adding to what has been said:

 

It may sound rather obvious, but "graphics suddenly going crazy" also could hint at a temperature problem or defective hardware somewhere in the system. If you get bright pink and green artifacts along with distorted geometry and such, it could be worth checking out the temps and run a few diagnostic tools. Since FSX is really abusing the CPU, especially if overclocked, temperature problems can easily arise if there is some clogged cooler fan or anything like that.

 

Debugging FSX with a multitude of add-ons can be quite a hassle, like a house of cards where you try to pull out a card without crashing the whole construct. So you decide if you want to troubleshoot your existing installation of the sim or start from scratch and re-install. In the latter case, a thorough cleaning of your OS is also in the cards, i.e. clean the registry and AppData folder.

 

So let's just wait for some screenshots and the video.