Crashes when connecting to a server?

[Emilyasdfgh]

Okay, so I have Linux/Ubuntu (just so you know), and when I open Tekkit Classic up and click multiplayer it says 'Connecting to server....' then 'Logging in...' (all the normal stuff) and then it disappears but the background is it still there. Then the mouse disappears, is goes into the server for a few seconds showing the chat and hot bar items but the surroundings are black, then it goes off again and back to the menu background then goes completely white and it's really really annoying because it doesn't do anything. I've tried deleting the folder and re-downloading, but I'm not sure if I've deleted the whole thing because I'm fairly new to Ubuntu but know most of the basics. Just wondering if anyone could help?

Just found out also that single player doesn't work either, it pretty much does the same thing but it just freezes when theres the hot bar and black surroundings.