I had the same problem with my DFP, I was in CTRA in a SO circuit, and I crashed a wall. In that moment the steering wheel started to make a rare sound, and I scared and disconnected the USB. Inmediately I connected again the DFP to the USB, but it didn't calibrated and my PC didn't detect it again... Now I am waiting 1 month and 20 days for a new DFP or a repaired one... I wanted to improve my skills in this summer holidays, but I only came back to my old DualShock
PD: Send it to Logitech saying anything... if you are in warranty time you can get your DFP repaired in Logitech.
EDIT: I forgot to say, that in the shop (MediaMarkt) they told me that in a month I would have my wheel working well... Now I'm waiting approximately 2 months ^^