Excel stops responding; then starts again

I have Windows 7 Home Premium, Microsoft Office 2007. When working on excel
spreadsheets, and I copy, then paste, it takes at least 40 seconds (which
seems like forever) and I get a message excel not responding. I can see the
circle spinning and after waiting long enough, the action works. This also
happens when I try to move contents from one cell to another and when using
format painter. I don't have any problems to date with Word.

This all started in the last 2-3 months. I have even uninstalled the
software and re-installed it and still have the same problem. First had it
only on the desktop computer, now have it on the desktop and laptop. One more
thing - I use an online backup, so the files are linked on both computers and
kept current. Could this be the problem? But, like I said it isn't happening
in other software programs or Word and all of the files on backed up online.

Can anybody help me?
--
LB