I was burning mid-night-oil yesterday while working on merging of 5-6 workbook on which my team has worked.
Suddenly at the last hour I noticed that all the options in Data tab is grayed out including filter and sort. I could not understand what happened. Today morning I found the problem and its solution.
Problem: The sheet was grouped with other sheets accidently.
Solution: Right click on on the sheet tab and select Ungroup Sheet from the context sheet.