blower fan would run all the time?

I have a 1998 Buick LaSabre loaded, 144,000 miles with climate control heat/air conditioner. During this past summer the air conditioner fan would run on an off for a period and finally would continue to run all the time until I would turn the ignition off. Now it is winter and the heater fan will not run at all. The hot air will still be blown in but no heater fan. Sounds to me like a problem in the computer. What is the problem and how can I make repairs or should I take it to the dealer and if so what will be the cost? Thanks
matadco