Skype for Business - Unable to open conversation window

Hello,

I have an issue with Skype for Business - it seems that the instant message windows are no longer displaying..

I mean each time I send a message to myself from a different account, no notification&no conversation window pops up. Same happens if I try to send a message to someone (I can search a contact and find them, but nothing happens when I double click on them to start a conversation)..

I already tried Office repair/reinstalled Office/deleted Skype data from %appdata%-Skype/deleted sip profile.. I am kind of stuck now

Do you have any idea on any other thing I could do or where this could come from?

Really appreciated, thanks!!