As we speak, we have a 1999 Buick Regal here for a coolant flush. On this vehicle you have to make sure and use a 50/50 mixture of Dex-Cool and water. It takes around 11Qts total coolant mixture. It would be a good idea to check and make sure you have coolant in your reservoir and radiator. Wait until the car is cool to inspect. We do pressure test, power flush and fill's here at Prestige Auto Works.
You need to check the coolant level in both the radiator and the coolant reservoir. If the system is full, I would suspect a faulty coolant level sensor. Very common for this type of sensor. This sensor can get contaminated with minerals in the coolant and "fool" it into thinking the level is low. The cure is to clean and flush the cooling system and replace or clean the sensor. Always use distilled water to mix with the concentrated Dex-Cool anti-freeze/coolant as Sacramento's tap water is very high in varying mineral content and reacts negatively with this special coolant. The color of Dex-Cool is orange, so if you have the green type or any other color, it also has the wrong coolant type in the system.