O.S. Windows8 MS Office 2013

My annoyance is the random indication in Excel onlythere was a problem sending the command to the program. Random means not all the times I click on the same Excel file. Eventually the files opens at the second attempt.

In Excel > Properties > Advanced > General there is a blank box that is to be filled up ..................at startup open all files in.............BLANK. I dont know with what.

Besides the above in the Registry my Keys read

HKCR Excel. Sheet8 > Shell > Open > Command that reads
[default] "C:\Program Files\Microsoft Office\Office15\EXCEL.EXE" /dde
[command] yh1BV5!!!!!!!!!MKKSkEXCELFiles>lVWA(TVkMAIS5Dh]3nVO /dde xb'BV5!!!!!!!!!MKKSkEXCELFiles>VijqBof(Y8'w!FId1gLQ /dde
[ddeexec] [open("%1" /ou "%u")]

I quoted the readings as the homologous keys with Word (that is OK) have different terminals
"C:\Program Files\Microsoft Office\Office15\WINWORD.EXE" /n "%1" /o "%u"

May I ask if there are suggestions at this regard?

Pls notice I tried already: DISM, reinstallation of Office, FIXIT and other.

Many thanks