@NLN 

Are you connecting to the SAME SSID? If 5GHZ, does the PC actually see that band and SSID? Can you connect to a different band?

Could also be the Security, possible the PC, especially if older, can't work with it? Will it work if you turn off the security.

Did you get any errors? Has the PC worked with a different router?

@NLN 

I have seen computers that ask for a pin rather than a security key. Look at the window where you enter the password and see if there is something you can click on to enter a network security key instead: