Conditional Formatting Problems for Excel 2003

I can no longer apply conditional formatting to cells in Excel 2003.  I have
half of the sheet formatted and have gone to format the rest of the cells but
have found that the conditional formatting option is now "greyed out".  I
have tried to copy and paste the formats also to no avail....

Conditional Formatting Problems for Excel 2003

Is your sheet protected if so unprotect and that should do it