Firstly, If your statement "No matter what network I am on" is accurate, then your internet service is irrelevent.
The issue appears to be specific to your computer.
Backup anything you want to keep safe, you most likely won't lose anything, but if you feel that something can not be replaced, copy it somewhere safe before you follow these suggestions.
Turning off Firewall and Antivirus programs will leave your computer un-protected while they are off. Once you find the problem turn them back ON to protect your computer.
The simple steps to try are:
1) The settings for your app may be corrupted, try un-installing the program and re-installing it. If you are asked by your computer to allow access for something, chances are it is required by your firewall software, say yes (ALWAYS read the notice carefully to see what it is asking).
Some programs will ask if you want to remove your personal/user settings. Say NO if asked. If the issue is not corrected, remove it again, say YES and re-install.
2) Turn OFF your firewall, and try to log in
3) Turn OFF Windows Firewall, try to log in
4) Turn off your anti-virus, try to log in (Your anti virus MAY scan all internet traffic to help protect you, stop this behavior for now).
5) Your HOSTS file may be re-routing the network traffic internally. If you installed something like Spybot Search and Destroy, try removing the immunization and see what happens.
This is just a starting list. With out more information, I can not be more specific.
If you find your solution, Please reply with what it took to fix this issue so others may also fix theirs.