people,why you do such a crazy things?
first I tried to reinstall RGSC from DVD but was totally uneffective,then I used system restore(from start\accessories\system tools)and took my PC back to the time of installing bully,everything fixed,But why bully did that,huh?
more than likely, Bully used a file that GTA4 uses, that 'got erased' when you uninstalled Bully. So when you tried to install GTA4, it was missing a "common file" being accessed by both.
good to hear you got both to work.