Problems with AF on 350D

I sent my camera in for a clean on Monday. There was a bit of dust on the sensor which was "blown-out" by the service people. However this morning I have been playing with the camera and I cannot achieve AF with the center focus point (I have a Canon 350D). I have tried with various lenses and all give the same result so the problem MUST be with the camera. Could there be some sort of damage? I have tried all other focus points and they are fine - but I cannot get focus confirmation on my center point.

Please help