I have an odd problem. My Epson Stylus Pro 9000 was working fine and then one day it just stopped working and only printed overlapping lines. I tried printing through both the computer and the printer's own utilities, but I got the same result each time.
Any help would be greatly appreciated, thanks.

If it prints all the lines of the file-page in one line on the page, making a black stripe on a white page, then something's probably wrong with the linefeed stepper motor or the electronics which drive it. That's a repair-or-replace issue to take up with the Epson service center; hope it's under warranty.

Do check the cabling first, just to make sure. A parallel-port printer cable that's just a little loose can drop just enough characters to drive you crazy.

Also, assuming you have or can find the manuals for that printer, doublecheck whatever switch or menu settings the printer has, to make sure nobody's recently changed how carriage-returns and line-feeds are handled by the printer. Also, if by "the printer's own utilities", you're referring to programs installed on your computer, check the settings there for the same possible recent change.

If the printer will print out a test page all by itself even while unplugged from the computer (my HP will), do that: that'll tell you whether the problem is in the printer or in the computer-and-cable driving it.

Thanks