1st suggestion
Verify that password. Every one makes mistakes... fortunately, passwords have zero tolerance for mistakes :) Also, make sure the security type is correctly set (WPA, WPA2, WEP, etc.)
2nd suggestion
If you own other devices that ARE able to connect, check their gateway, subnet, IP, DNS information and try manually setting your laptop with the same information but w/a different IP. Verify there are no other devices on your network fighting over the same IP address. (If you don't own any other devices, hard wire your laptop with an ethernet cord and note the same information then manually set the WIFI connection)
3rd suggestion
You may have possibly installed another kernel during an update/upgrade that broke your wireless. First open up a terminal and type:
uname -r
Write down the output on paper or other device. Next, type:
dpkg --list | grep linux-image
If you see more than one kernel installed: reboot your computer, but keep pressing Shift as your computer is starting so you can get to your GRUB menu. From there, use the arrow buttons to select a different kernel (than the one you wrote down) to boot from and see if anything changes.
BTW
Do you administer your router?
Also,
Have you tried booting from a live cd/usb & trying to establish a WIFI connection?