This is a common problem on the Buick Reatta. Here is how it is usually described:
The CRT and Instrument panel are operating on RAP and are not getting power as they normally do. The problem is usually caused by a bad ignition switch (located at the bottom of the steering column) or a blown fuse or bad RAP relay. Location Of Console Fuses And Breakers
The CRT (touch screen) is blank but when I push the radio button on touch the screen, where the on/off button would be, the antenna will go up and the radio will come on. The radio has no memory other that the factory presets.
There seems to also be a short somewhere because when I shut the engine down and get out of the car, and shut the door, the interior lights come on and stay on. So I open and close the door until they shut off. When they do shut off, finally the dashboard lights will come on. The test button triggers when its done doing the test the dashboard lights go out."
R.A.P. - Per FSM section 8A-15-3
Retained Accessory Power (RAP) System provides power to operate several vehicle accessories after the engine has been running and the Ignition Switch has been turned to OFF or LOCK but before any door is opened.
Systems involved - Power Windows, Sunroof, Radio Wipers, GloveBox Light, Overhead Reading/Courtesy Light, and Tonneau Release for the Convertible. All of these are powered for ten minutes after the Ignition Switch is turned to lock.
BUT - Open any door and RAP is de-energized.