Getting "Connection Failed" Error while trying to connect to WiFi network

I'm having problems connecting to WiFi networks. After entering the required password I'm being redirected to the same panel that I've entered my password on with a little error message at the bottom left saying "Connection Failed". I've tried setting up my phone as Hotspot and connecting to it from the computer. It sometimes works but mostly does not. With this insight I think the problem might be system-wide. I'm experiencing some delays when I click on the WiFi icon at the top. That supports my conclusion as well. I've tried resetting everything; forgetting network and connecting again, disabling Bluetooth. I've even reset my modem but nothing worked. What do I need to do? Thanks in advance.