Are the clips locked?
Select the clip(s) > Right Click > Lock... I think.
Otherwise you can check in the Inspector...
Select the clip/track > Opene Inspector (press I) > Select the Clip tab at the top of the Inspector and then look where it says Lock. If it says Pos or Data or Pos/Data click that section and choose None (or whatever it says there) to unlock the clips.
Then you should be able to slip edit them.
If they aren't locked then I have no idea why you can't drag the ends.