Yukon Air Conditioning Problem

[borninski]

Vehicle:
1996 GMC Yukon GT 4x4, 5.7L (350)

Problem:
When I acquired this used vehicle, I noticed the air conditioning wasn't fully charged and it was blowing luke-cold air from the vents. Everything was working fine and operational, aside from the fact that the air was not very cold). I stopped using the a/c because it wasn't that hot outside, but before I ever had a chance to get the a/c serviced, something must've failed in the system.
Now, all that works is just the actual fan motor. I always left the position on the ' (all the way to the left), and now it's stuck that way and only blows air from the floor vents. Even when you try to turn the dial to get the air off of the floor vents, the air continues to blow from the floor vents when the blower motor is turned on, regardless of the position of the selector. Also, the actual A/C button does not work (the light does not illuminate and the compressor does not kick-on anymore...same problem with the other 'air circulation button').
I checked the A/C fuse under the hood and everything looks fine...I am decent with working on cars, but I must admit that I know nothing about air conditioning or electrical systems, so any and all help you could offer would be most appreciated. Please feel free to reply and also let me know if I can answer and questions or clear anything up for you (I know that it might sound confusing without a visual...the Yukon that I have has the standard Chevy/GMC climate controls for those common model years).
Also, I will take any recommendations on where to take the vehicle to get the A/C system serviced (I live in the Dallas, TX area).