C&C series is riddled with compatibility issues, for example using ddraw on the "original" engine (original/tiberium dawn, ra1) is the difference between playable and broken on many systems. ra2 seems it can handle any resolution upto 3840x1620 (4k is actually 3840x1920) (my experience)
try the community patch sets, it brings mod support back to generals and zero hour, not sure of "newer" games (c&c3, ra3).
just make sure you turn off origin's cloud sync for each c&c title, or it'll "repair" it back to stock.
as for the actual issue itself, it's likely you changed the resolution to something "unsupported" the community patches usually support higher res... but the base games can be a bit iffy. access your generals save data folder and "rename" it by adding "BACKUP" to the name...
this should allow you to boot the game as a fresh install. if it's a setting, it'll work until you mess with the settings...
for future reference, gaming problems need basic info, like hardware info
(e.g cpu = intel or amd and model of cpu. Ram amount, graphics card brand and model operating system (usually windows 10 now), all i'm doing right now is guessing your issue from the annoyances i've seen.
