Next step is to make sure you are typing in the correct code and character set, Capitals, Upper Case letters, and the like.
Usually the newer routers have the WiFi password printed on a label someplace on the routers case. That is unless you changed it.
You can get the correct code from a PC running Windows 7 that is presently connecting to your Wifi. At the present I don't have a WiFi Win 7 PC at my disposal so I can't look up exactly where but it is in either Manage WiFi connection or in the properties of the WiFi card in that computer. There is a Check box to "Show Password".
Then again most of the newer routers also come with this WPS system, Wifi Protected Setup, and if you never disabled that on the router and typed in your own password you might try that if the printer is equiped with WPS.