How to troubleshoot a printing problem?

[joe at actionline.com]

I have an HP LaserJet4 that has worked fine for years printing via 'cups'
from my long reliable Linux box.

But recently it started hanging up with the "form feed" light lit and when
I would tap the "form feed" lighted button, it would print a single
document.

Then, a couple weeks later, that quit working and when I would tap the
"form feed" lighted button, the printer would just print a page with a
single line that reads:

;%-12345x'pjl set pageprotect=auto-*'pjl set manualfeed=off*'pjl set
economode=o...

I am able to print a test page from the printer, so I believe the printer
itself is okay.

When I go to http://localhost:631/admin/ (there is no login to root, as I
understand there is supposed to be), but it just opens to the admin page
automatically ... but I am unable to delete either of the printers listed
there.

Meanwhile, I have been able to print from my wife's xp laptop.

And also, I have been able to print from another laptop on which I just
installed kubuntu.

So, I assume the problem is something wrong with 'cups' on my main desktop
computer

How can I trouble-shoot this and figure out what needs to be corrected?