I had the same issue and solved it (Dunno if it's temporary)
I went to the advanced settings as was suggested earlier and it was using Javaw.exe to launch minecraft, I changed it to Java.exe and it's now working smoothly (So far)
Hey, I used to have this same problem. Make sure you don't accidentally have port 25565 on port filtering instead of port forwarding in your router/modem.
I had the same issue and solved it (Dunno if it's temporary)
I went to the advanced settings as was suggested earlier and it was using Javaw.exe to launch minecraft, I changed it to Java.exe and it's now working smoothly (So far)