Hello Dennis, my name is Dan.
I will do my best to help you, the only stupid question is the unasked one.
Your iMac just needs some TLC (tender loving care). Some of this works best with an attached USB keyboard, any USB keyboard Windows included.
First I suggest repairing permissions, this will not affect Excel but will help the whole system and may stop the beach-ball by itself.
Repairing Permissions That is a PDF explaining what they are, what they do and how to fix them.
Next is a pram reset.
To do a PRAM reset, you need to restart your machine and hold down these 4 keys all together at the same time.
‘Option’, ‘Command (Cloverleaf or Apple)’, ‘R’ and 'P' all together at the same time.
Keep them down until you hear 4 startup chimes, this is the sound that your computer makes when it starts up, it is like a boonngg. The screen should also cycle from white to black and then back to white along with the chimes.
The sound should also get louder.
If you have a wireless keyboard then the procedure is a little bit different.
Use the very same keys but wait until the first chime and immediately press and hold those keys. I recommend getting your fingers ready because timing is critical.
It can take many try to get it, any USB keyboard is preferable.
If using a Windows keyboard then substitute the Control key for the Command key and the Alt for Option, all others stay the same.
This resets all of the system buses on your computer, USB, FireWire, display, ethernet and your keyboard/mouse/trackpad.
This will correct many faults but not necessarily yours.
Then, last but not least, a SafeBoot, again the USB keyboard makes this much, much easier.
To do a Safe Boot, restart and before the first chime press and hold the 'Shift' key.
Wait until you see the Apple logo and the spinning gear appear, then let go.
It can take as long as 20 minutes to load, so please be patient.
When the login screen appears it will say in red on the login window 'SafeBoot'.
Now login and give it a few more minutes to finish loading.
Try doing whatever it was it was giving you the problem. If it works then probably the problem is solved, so restart normally.
If the problem persists then restart normally also, other fixes will need to be done.
That should set things right, this widget for your Dashboard is nice for keeping things good without hassle.