My guess is that you may be pressing the AS button and turing on the radio without first having turned on the ignition !
If the Radio says SAFE then turn on ignition first and try again.
If the Radio shows a number and SAFE ie: 7 SAFE
Then thats how many goes you have left, and there will be a penalty time that must elapse with the radio switched on as this counts down.
Generally
Code Entry as Follows:
Turn Off Stereo
Switch On Ignition (No Need To Start Engine)
Press & Hold Preset " AS " and
Switch Radio On - Display Shows
" SAFE " And Then Shows " 10 - - - - "
Press preset " 1 " repeatedly for 1st Digit
Press preset " 2 " repeatedly for 2nd Digit
Press preset " 3 " repeatedly for 3rd Digit
Press preset " 4 " repeatedly for 4th Digit
If the correct code number is now shown
Press & Hold Preset " AS " Until the Unit Beeps