Help Needed

[xDeadxSnoex]

Ok, so I can go into the launcher for tekkit just fine, but when I try to play a previously made and saved world it gets to the loading and building chunks screen then it stops. It sometimes goes unresponsive or it will just stop. My computer is not freezing up because I can do other things when it is trying to load. I also can create new worlds just fine, but when i try to reopen any then it just gets stuck on that screen.