Why is filter forge flashing?

Guess no-one can guess why since you have no details of what is going on aside from flashing....Such as operating system, what else is running on the system, what version of FF...etc....Treat these type of situations like toast......In order for someone to create the same piece of toast that you made you must explain in detail how you made that toast........This requires what type of toaster you used , the bread used, how long you toasted the bread and what type of butter....etc.....
Explaining in this fashion (detailed) most of the times leads to better outcomes than just saying you made toast.....

If no other programs cause this flashing/flickering, I would:

1) Close all programs, power off the machine.
2) Bring it back up and see if the problem still exists.
3) Check and see if you have the latest video drivers for your machine. Also, make sure that the refresh rate for your display is correct.
4) Uninstall Filter Forge, then reinstall it. It should save your presets, but for good measure you should back up your important files if you get to this step.

Hope this helps.

Unfortunately, all I can give you as an example is the way I do it in Windows 7:
I right click over the open desktop, a menu is provided which usually has a video control panel (or at least a place to change/view monitor setting and resolution) for the company that made your video card. My Windows 7 machine has an NVIDIA card. The refresh rate and resolution etc etc should all be in the video control panel if you can find it.

You might want to consult with FF support directly before reinstalling. Maybe they know something about this I don't know...

I have a NVIDIA card too, but have no idea what the settings should be. What gets me is it's bee working fine until know.

What should the settings be?

It was just crashing. No error message. Restarting didn't solve, but shutting it down then turning it back on seemed to remedy it. Not sure why the difference. lol