I had a former in excell which highlighted cells with a colour if overdue. The file's become corrupted and I don't seem to be able to find my backup.

The event happens every 3 months, and annually a different event before resuming to event 1.

So event 1, event 1, event 1, event 2, event 1....

Within 30 days of an event deadline the cells went orange, then red when due or overdue.

Basic cell arrangement was

Name..... Address 1/2/3..... Postcode..... Date of last event 1..... Next event 1 due..... Date of last event 2..... Next event 2 due.....

Can any excell guru's help me remake this?

Look up conditional formatting using a formula in the help or google.

WHich Excel? Have you done anything stupid like updating from 2003 to 2010 and saving as an xlsx rather than an xls?

No the whole file is corrupted and generates an error.

Tried 3 machines and my tablet. None will open it

Conditional formatting is what you need.

"Home" tab on the ribbon, and then about 2/3 of the way across, iirc.