I am assuming you are talking about Excel 2010 version. In most cases you will need to just close Excel workbook and re-open it again. If that does not work, try few more times closing/re-opening. If that does not work, then you can try uninstalling PowerPivot, restarting machine and installing PowerPivot.
I'm running Excel 2010 and have seen this greying out "often". When it happens, I get the button active again by "simply" uninstalling, and then re-installing the add-in "PowerPivot", as Vidas mentions.
1. File-> Options -> Add-ins -> "Manage" -> (dropdown and Select): "COM ADD-ins" -> "Go" 2. In "Com Add-ins" Pop-up box, UNCHECK "PowerPivot for Excel" -> "OK". 3. Then reinstall PowerPivot by repeating the sequence. 4. File-> Options -> Add-ins -> "Manage" -> (dropdown and Select): "COM ADD-ins" -> "Go" 5. In "Com Add-ins" Pop-up box, CHECK "PowerPivot for Excel" -> "OK".
I'm able to do this without having to restart things. (Do this a few times, and you get pretty fast with the sequence )
Comments
What should I do?
1. File-> Options -> Add-ins -> "Manage" -> (dropdown and Select): "COM ADD-ins" -> "Go"
2. In "Com Add-ins" Pop-up box, UNCHECK "PowerPivot for Excel" -> "OK".
3. Then reinstall PowerPivot by repeating the sequence.
4. File-> Options -> Add-ins -> "Manage" -> (dropdown and Select): "COM ADD-ins" -> "Go"
5. In "Com Add-ins" Pop-up box, CHECK "PowerPivot for Excel" -> "OK".
I'm able to do this without having to restart things. (Do this a few times, and you get pretty fast with the sequence )