From what you've described and posted, it really seems to me that the computer is hanging on launch because it is still attempting to find and start MacKeeper, which is long gone. Somewhere in the bowels of the computer, there's something that's instructing Mac OS to locate and start MacKeeper.
One of the things that MacKeeper does is it creates a login item in your Keychain. If you have searched the startup items in the Users preference pane and you haven't found a reference to MacKeeper (or to a program called helper.app, which is its startup file), try opening the Keychain Access program in your Utilities folder and search for anything referencing Zeobit, MacKeeper, or helper.app -- remove anything you find.
Still no dice? Re-install MacKeeper (the demo version should do nicely), restart your computer, then uninstall MacKeeper using the procedure
here.
