Banana3-3

Hey everyone I'm having some trouble logging into a voltz server I was playing on recently, and I'm not very good with computers, so I was wondering if I could get a little help. Whenever I try to log in now, all I get is a blank page with the dirt blocks as the background, and the 'done' button at the very bottom of the screen. Previously when I tried I was getting a message on a blue screen that said that minecraft had crashed because of a 'ticking screen,' I think. I've tried getting rid of the launcher and re-downloading it twice (making sure I cleared all launchers), and I know I'm using the correct version. I'm not getting anything from it. Again, I'm not very good with computers, so I may be slow to pick up on some things, but some help would be very much appreciated. I'm using a Mac OsX version 10.8.3. Thanks!!