2004 saab 9-3 electronic key won't work

Try to unlock the trunk door.

Or call the dealer and provide them the VIN so you can cut a new key.

Saab have an auto-lock to thier trunks. So that nobody else can open your trunk while you're in the car etc. If you open and then closes a doot the lock should unlock. If not, your modell is only unlockable with key/doorbutton.

The doors work on a different system to the ignition. The doors will unlock but the ignition key immobiliser is specific to each car. That means the car won't recognise the key. Replacing the lost key would have been the easiest fix even though it costs a lot. All you need is the vehicle details for your car. I was quoted £200 for a replacement Vauxhall key. Cheaper than replacing steering columns and associated electronics.
Your only other option is to take it to a Saab Dealer/specialist and pay the 'silly money' for them to reset and link the replacement scrap car key to your car.

check trunk fuse

Hello. The electronic opener needs new battery. Change it and it will open. The dealer can get you a new key. Get the Vehicle Identification Number & Bill of sale or good proof it is your car and they will help you get a key.

Saab's have very specific steps that you must follow when you change the batteries in your key fob. You might try these steps to re-sync your key fob to your security system....

If the battery has been changed outside the
car and the car is locked, proceed as follows:
1 Unlock the front left door with the traditional
key. If the car has a car alarm, this
will be tripped.
2 Open the door and insert the remote
control into the ignition switch. If the car
has a car alarm, this will be silenced.
The remote control and receiver unit are
now synchronized.

hello, did you solve your problem? maybe its same problem as this?
http://www.fixya.com/cars/t2779855-saab_93_keys_not_working

If the fuse is okay, check to see that the latch is not bound in some way, and that it is properly lubricated. A dry latch sometimes will not release.

replace the battery in your FOB (your key)
your key has to talk to the computer for it to start
if your battery is dead in your key it will not start

Does the key still pop the trunk/hatch? That would also indicate whether or not it was the key remote. If that function works it's probably nothing on the car (i.e. "receiver") end.

There is a very good SAAB forum that would likely be the best place to find out if somebody has has this issue before and what they have done: www.saabcentral.com