Can't write anything in the "this workbook" window of the vbe
 

Help! No matter what i do, excel crashes when I try to put any code in this
window, telling me that "Excel has encountered a problem and unexpectedly
needs to quit." Nothing is password protected, so that's not the issue, and I
can't even get far enough to put in a line of code because it crashes as soon
as I break to a second line. (I've tried pasting a macro I know works from
another workbook into this one, and the same thing happens.)

Does anyone have any ideas? I'm getting desperate.