Then it's probably not really available for your printer. I'm not sure how old that one is, but HP hasn't had good support for really small sizes for most of their run. If you still have the documentation for your printer, check to see the minimum size and minimum printable area.
The problem I've found with some of the HP lasers is that they can feed the small cards fine, but they can't set up a minimum printable area in the right place for where the paper feeds. (In other words, it's probably printing, but beside the card, not on it.)
Try running a letter sized sheet of paper through (with the 3x5 size selected) to see if it's putting down toner anywhere.