This article is from the Spreadsheets FAQ, by Russell Schulz casfaq@locutus.ofB.ORG with numerous contributions by others.
check your International settings in Control Panel. when these get
corrupted, Excel will still use them, with ugly results.
10.12 How can I add 14:00 to 14:00 and get the cell to say 28:00 instead of 04:00? (spreadsheets: Excel)
> For Excel 5, 7, 8
> format the cell: [h]:mm
>
> Excel 97 makes it easier now, by including the format among the pull
> down choices for a time format.
 
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