HP Laserjet 4250N issues any ideas???????

Hey everyone, here at work, and we've got a couple of HP 4250N Laserjets giving issues. First of all, not really noticing any error codes or anything of that sort, need to research more, but this problem is occurring both on Windows and Macintosh systems. What's happening is that sometimes these printers do not want to print, or sometimes they just do their own thing. In other words, you tell it to print, it may not print, but may print 30 minutes later, or may print when the next user prints a job. Just basically when they feel like it as it were. Anyone have any ideas? These are networked and hooked up by IP.