mine did that..the antenna or whatever its called failed..manually unlock the car..ign on and enter your valet code.
there should be a switch on the dash or console that has two buttons..you enter your secret code into that with the ign on if you never changed your code it will be in the handbook...have a look on the clifford site
2 button valet switch. star button and blank button. lets say your code is "1 2 3 4" ......switch on ignition, press start once then blank to enter, star twice then blank to enter, star three time then blank to enter, star four times then when you hit blank alarm turns off. if you keep blank press for 3 seconds or so, alarm goes into valet. will drop out on next ignition use.