Buick Repair Questions? Ask a Mechanic for Answers ASAP
This has the PASS-KEY system in it. Are you familiar with it?
Do you have a spare key to try?
Here is some info on that system for you to read. Be sure to check the fuses and make sure the resistor pellet on the key is in good shape. Most likely it's either a key lock cylinder or the Pass Key module are at fault.
As a last ditch effort, you can try turning the key on for about 10 minutes until the sec. light goes off, then turn key off, wait 5 seconds or more then try to start it. This will relearn the pellet resistance to the module....worth a try, otherwise a shop will need to test the complete system. If you have further questions feel free to reply.
Here are the key pellets.