If it's the 00 and up (may include 99 also), you need to punch in the code number thru the radio. Code number is in the manual packet sleeve on a card if not lost. You can buy them on websites with all your car info. Happened to me twice (I have my card though, so the fix is about a minute), but don't listen to all the ways to get at the cable and unlatch it, you'll mess up something. It's an electric/cable release lever, these won't unlatch manually only w/o creating a probable issue. Some wierd anti theft idea Porsche had back then.
Dealers can do it too, for about $300.