All of a sudden, I cannot access my Yahoo Messenger. It pops up the sign on screen, then I sign in but it immediately flashes from "Welcome ScrappyKi" to grey sleeping smilie with my contact list greyed out.

I have tried to reboot. Remove and reinstall. Changed the firewall/proxy choices (i.e. no proxies, use proxies, firewall no proxies, firewall use proxies) with no luck.

I'm at a loss!!!

Did you try a System Restore? Probably too late now if you uninstalled/reinstalled YM.

When you uninstall it is very important to not only use the Uninstall feature but to then do a Search from start/search/yahoo and delete all finds. Then run a registry cleaner and remove all Yahoo entries as well as all green light issues. Here is a good free cleaner:

http://www.hoverdesk.net/freeware.htm

After all that reboot the machine then try to reinstall the messenger.