Dear Ramesh
I would like to thank you very much for your hint
I could not start Oracle on my client application test machine anymore, somehow I found out that there is a problem with the eventlog and then was led by my friend Google to this
page which not only helped me to start the Windows Eventlog again but also (as a consequence) to be able to work with Oracle again.
Renaming this folder was IT!!!
I was afraid I would have to reinstall Windows over the weekend... which is not necessary anymore
Instead I will fill a glass with a good wine and raise it in the direction of where I think you are and cheer to you.
So let me repeat it:
THANK YOU VERY MUCH !!!!!