unable to add comments to a cell

[alpine4133]

Excel 2007
Sheet and workbook are not protected.
I was able to enter them earlier today.
Now the option to add a comment is just not available in any cell.

 

[shift-del]

Hello

Did you group worksheets?

 

[alpine4133]

Hello

Did you group worksheets?

I do not know what happened. All of a sudden everything locked, many things I could no longer do. How can I ungroup? I do not know what grouping worksheets even does. Maybe I hit the key combination by accident.

 

[shift-del]

How can I ungroup?

Right click on a worksheet tab.
There should be somehting like "ungroup worksheets".

 

[alpine4133]

Right click on a worksheet tab.
There should be somehting like "ungroup worksheets".

That was it.... Thank you so much.
Can you tell me what is the purpose to Group tabs or sheets? Especially since it disables functions.