Port forwarding failing for no obvious reason?

Ok, here's the problem: something is wrong with my computer or modem/router, but I have NO clue what is causing this problem. I have been trying to set up a server for mumble/risk of rain/Gmod/minecraft/etc for the past few weeks and it has not been working, even though the last time I did this (a few months ago at most) it went off without a hitch.

I tried:
disabling my firewall (completely)
disabling my router/modems firewall (completely)
enabling DMZ
(All these are now enabled/disabled now, so don't worry about it, it was just for testing)

And it did not help. I checked my problem with canyouseeme, and I got port 80 to respond when I had my firewall for public connections disabled, but with any other port (say 64738 for murmer) it says connection refused, try to connect to the server through mumble? Connection timed out. This is with all the steps taken above, and the only one that makes a difference is the public connections in the firewall, which if it's enabled it just says connection timed out instead of connection refused on canyouseeme and no difference in anything else.

I'm just tired of this and have no clue what to check for now. I have to assume it's my router, since I got a new one a few months ago and this started happening, but I also reinstalled my OS around that time and lost all my firewall changes I may have made and the windows firewall is the only obvious thing that seems to affect anything.

Guest

Connection timed out means that nothing tried to respond to the incoming packet from the test server. The incoming packet was simply ignored.

Connection refused means that there was nothing capable of responding correctly to the packet and the incoming packet was rejected. Typically, a computer will refuse a connection if there's no server process attached to the specific port that the packet is addressing; however, it might also occur if the server process is not running correctly or the process does not recognise the packet's contents.

Some ISP connections do not allow you to access your computers using your public IP address from within your own ISP connection. If your ISP has this restriction, you have to test the connection from a different ISP line. I test my servers using the Internet connection from my smart phone (using mobile Internet and not the Wi-Fi connection).

Richard