Hard time doing basic commands

This is an example of one problem I'm having (trim).

1- I have selected the breakline to trim the yellow line (3) to.

2- I cannot move up to pick the yellow line (3) to trim it. The "Locate Tolerance" circle just slides across the screen.

I seems this isn't always the case. When I first open the file I am able to execute the trim command w/o any problems then suddenly it doesn't work correctly (what I'm used to). The same problem occurs when I try other simple commands.

Is there any way to address this problem?