The phone should respond to the codes, even if you have a wrong code it should say something like wrong code, the only reason it might not display nothing is either if your typing in too few numbers or its not been entered correctly...
Either turn on the phone with a working sim card in the phone, wait till its started up and shows the network logo and lets you dial numbers and then enter the code
Or
Insert an incorrect sim card into the phone, e.g if its an Orange phone, insert any other sim other than orange and the phone should display "Enter Restriction Code", when it displays that enter the full code...
The + P and W keys are entered using the * key repeatedly...
Code should be *#PW+15 Digit Code+7#
Remember not to enter the spaces between numbers these are only put in to make it easier to read on the calculator
Which phone are you trying to unlock please???