What OS are you using?
I have one which I just connected to the parallel port and started Win2k - it was recognised and installed correctly and works fine. So I am wondering if you have installed any special software from the HP site or install disk?
Try going to the printers applet and remove this one and install again.
As for how much toner is left, I don't know how to tell - it has run off thousands of pages of text and so far the quality is as high as ever.