I had the same problem after endlessly checking that I entered the password correctly. Tried in uppercase, lower case and mixed case as detailed on the router - all to no avail. This was from my desktop PC. I then tried pressing the wps button on the router and this allowed a connection between the router and my PC without the use of the password. I could then enter the router and change the password to something I could remember. This worked OK and I could then connect my other devices using the new password. Maybe this will help you - fingers crossed!
Which is useful only if the password printed on the label under the router is correct, and someone has changed the password on the router.
WPS, as recommended by @forestdweller, avoids this happenstance.