3D Analyst isn't working

[KatharinaStein]

Good evening,

I have a problem with the 3D Analyst. I would like to use this to create a profile diagram to show the differences in altitude of the river.
However, the tool is grayed out and no action possible.
Can someone help me?

[JayantaPoddar]

Have you enabled the 3D Analyst from (Customize > Extensions) in ArcMap

[KatharinaStein]

Yes I have, This is unfortunately not the problem.

[JayantaPoddar]

Could you close ArcMap and open ArcCatalog (standalone), and enable the extension there also (Customize > Extensions). Close ArcCatalog, and open ArcMap once again. Add the DEM Raster. Does it work?

It sounds silly, but sometimes it works.