Unable to connect to world

I wanted to play with my friends so I opened the server. it seems to work fine at first (it was my first time to play in windows edition) but when I tried a second time my friends couldn't join my server saying "unable to connect to world" on their screens. 

I thought maybe my firewall was blocking so I turned it off.....but it still didn't work. I don't think my account is the problem?? My phone works but not on my computer.

I tried to fix it but no... never solved

can someone help??