I have been using Excel for quite awhile but have not run into this issue. I have Excel 2010 and Windows 7.
One of the main spreadsheets that I use has developed an annoying, quirk and time-consuming problem. For no apparent reason, groups of rows become Hidden. They seem to do this all by themselves (at least I do not do anything and the spreadsheet is not shared)
When I notice that large groups of rows are hidden, I have to manually unhide each row. I am not able to select the one before the missing block and the one "after" the block and do unhide. Nothing happens. so one by one I have to do the unhide.
HELP .. this is very time consuming.