Blank page at startup


I successfully installed elgg in my MAC using mamp.  When i installed additional plug ins (the popular ones), it worked ok the first time around but then the nightmare happened.  I installed a plug in called invitation_02, when i logged in, all I saw on screen was an error message telling me that the invitation plugin is erroneous.  I couldn't get back anymore to the login page no matter how many times I restarted the computer, cleared the cache, cleared the history, etc..  So, I went into the root directory and manually deleted the invitation plugin folder.  Then restarted the computer.  I didn't get the error message again but I also have no more login screen.  I only see the background theme and a white window in the middle of the screen where the login page should be.  Would anyone of you experts please help me resolve this?  Do i need to reinstall elgg?