D300 shifts to one point focus

Johnsonran, I have the same problem. Suddenly the camera stops focusing, changes to single point focus, f stop changes to f/0.0, exposure changes to aperture priority, metering changes to center-weighted average. Photos turn out black. Have returned the camera 3 times for repairs on warrantee. Took home a loaner, changed the settings, practiced a few shots, and the same problem happened immediately with the loaner! I was told the issue may be the 51 focus point feature. Now I am waiting for a brand new replacement, but will I have the same problem? I few days ago, I shot a wedding using 21 focus points with no problem. Try that.