Is there a Vista driver for the 5L. My 5L works OK on XP, but it is an old laser printer these days - Look at the HP web site. You may find HP will not/have not produced one for this old printer? Incidently mine is still printing well.
Just in case - I just remebered I use the HP 6L driver on my XP PC, as I had probs with the 5L driver.