Try this:
ViperMkVII:
You can also try this method:
Unhook your game so you can start your game normally;
After having started your game, switch to the desktop, then start C&C:Online, and click the RA3 button inside the launcher.
Then you should be able to log in in the game (but if it failed, the log in will fail with message of "Cannot connect to the backend server").
If that doesn't work, you can try to end RA3.exe process with your task manager (If you are using Windows 8 /8.1/10, do not end the process called "Command & Conquer: Red Alert 3" in the process tab, that would terminate the game; Instead, go to Details, find the process called RA3.exe and end it) before starting RA3 from C&C:Online launcher.