02 allroad suspension stuck on level 1
 

My Audi Allroad's front wheels are practically touching the top of the wheel wells because the front is so low. When the car is turned on the compressor comes on for about a minute before turning off (The compressor makes noise and shakes, but still could be bad, not sure how to diagnose this). When driving, the suspension light on RPM reader remains on. When the car was on the ground, I was about to reach in and touch all the airbags, and found that the front passenger side was flat and noticeably had no air in it, while the other 3 where firm and seemed to be filled with air. Would one airbag being flat cause the whole suspension system to not work? I am trying to avoid paying the dealership $100 for a diagnostic so anything helps!!! Thank you!!!!