To whom it may concern (Nessa)
How to fix the error: LIVE Gaming on Windows failed to initialize. This may be because another LIVE Gaming on Windows application (such as the Halo 2 dedicated server) is running on the same machine. Otherwise, reinstalling the game may fix this problem
Steps:
1. first of all go to control panel and programs and features
2. Uninstall games for windows client software if it's there. If it's not there skip this step. If you uninstall it then restart your pc.
OMG, sorry for being late to help fix this issue. I wasn't on Xfire last night due to celebrating Eid with family, friends, and relatives. Also yeah, I remember having that same problem before when I reinstalled Halo 2 Vista on my old computer with Windows 7 back in 2010. So the main solution for this problem is just by downloading the Games For Windows Live client from Microsoft website.