Konica-Minolta 2400 problems

I recently purchased a KM 2400W and from day 1 it smudged and overlaid in black and white mode particularly word documents. I returned it for a new printer and voila same thing right out of the box. It almost looks like the toner is empty however I checked the icon and the toner is full. Before I return and give up on this thing does anyone have any ideas for me, if not I will purchase another printer the down side to this is the KM 2400 was incredibly well priced for the package. Note KM help line was of little or no assistance.