the main difference between Lars and your issue is that JChemExcel contains 2 different addins,
1 is responsible for JChemExcel functionalities GUI, whatever.
2 is responsible JChemExcel functions, calculations, and special functions for drawing.
Lars could not get 2. working, your problem is mainly related to the 1. one.
And you do NOT have loading issue (which Lars had) because JCHem menu is there,
if the addin or addins are not loaded, then JChem menu cannot be seen at all.
And Excel/Options/Addin drops the addin to inactive or problematical addins. If your JChem menu is greyed out, it means that addin was loaded but erro migth occured loading the further part of the applciation e.g. .NET, or other component. If you check the log files in
C:\Users\<Your user>AppData\Roaming\ChemAxon\ and find reported errors logs in the CXN Loader folder or in the JChemExcel zou might see that what
was the problem before you repired the application.
There are common components shared between these applciations please be careful that 5.4 JChemExcel possibly cooperate with 5.4 IJC and 5,4 Marvin.
At least make sure that 5.4 not to be overinstaleld with 5.3.8 and so on.