For some reason, when I crashed out of Excel one time, I lost the capability
of toggling between workbooks in one Excel session. I can still do this for
powerpoint, word, etc, but cannot for excel. It's very frustrating becuase I
used this feature quite often.

I can open another session of Excel but when I have to move or copy
worksheets from one workbook to another I can't. I hope someone can help me
with this! Maybe it's an Excel problem or a Windows problem?