Plugin error, can't login or logout if plugin is activated

I can’t figure out why is my plugin doing this. I wanted to customie my admin login screen and I made plugin that worked perfect on localhost but it doesn’t work on my hosted website. The thing is, even if I leave only the plugin information code in the plugin code file, it still doesn’t work. But the same code is working on my localhost. Could this be some host, wordpress configuration issue? Help!, Thanks.