I installed Ubuntu 17.10 today. This is a PC and since motherboard doesn't have inbuilt wifi I attached a PCI Wifi Card.
When I installed Ubuntu it automatically detected the wifi card. it shows me all available networks.
But when I click on my network. It shows me a circle for 1 minute and then the circle disappears and it doesn't connect to wifi.
it doesn't give any error. (I am entering right password).
I selected the gear icon next to my network and I can see that its using WPA & WPA2 Personal and it has the right password. Everything else is set to automatic.
I am using this wifi card
https://www.newegg.com/Product/Product.aspx?Item=9SIABG954D3777
Edit: I formatted the hard drive and installed windows 10. and windows 10 connected to wifi without any problem. So clearly Ubuntu has a problem with the PCI wifi card.
Try restarting the network manager service.
Also, I know it's a longshot and you said otherwise, but
cd
to/etc/NetworkManager/system-connections
check the relevant file of your wifi connection to see whether the saved wifi password is different than the one you are entering.