http://h10025.www1.hp.com/ewfrf/wc/d...cname=bpd09143
Assuming that you've done all the things listed in the above web page--
And the printer works properly when connected to another computer.
The problem may be related to the USB system.
Usually, this problem (If software related) can be solved by uninstalling (not deleting) the printer driver, then Rebooting, and reinstalling the printer driver before you connect the printer to the USB port. Make sure that the printer is connected to the first USB port if you have more than one port. If this doesn't work, the next step is to uninstall both the printer driver (again) and the USB controller and port drivers. Reboot from power off with the printer disconnected, allow the USB drivers to install. Reboot again, and install the printer drivers, following any instructions given by the driver install. Normallu, the printer is not connected to the USB port until called for by the driver install.
A reboot normally automatically reinstalls the USB controller and port drivers.
Note: some systems use a support chip set that requires drivers not suppled with windows. Thes drivers may usually be obtained from the MBD mfr, or possibly the chip set vendor.
(If the computer uses a USB interfaced keyboard and mouse, you may want to have a PS/2 style mouse and keyboard available if the USB port and controller drivers are uninstalled.)

If older printer drivers were installed on this system, and SP2 was installed, it's possible that this was the source of the problem.
If the following from the HP support does not work, the problem is likely in the printer-- (assuming that the 815 behaves like the other printers in the series)
HP Deskjet 810c, 825c, 830c, 840c, 845c, 880c, and 895c series printers
Running a sample page
NOTE: This test does not work with the HP Deskjet 6830v and 6840 series printers.

1.. Turn the printer on.
2.. Press and hold the RESUME button until the printer starts printing.
3.. Release the RESUME button.
Running a diagnostic test
1.. Turn the printer on.
2.. Press and hold the POWER button.
3.. Press the RESUME button four times.
4.. Release the POWER button.


"rawhide" wrote in message ups.com...
I have a 815c printer that pretends to be printing (cartridge moving
and all) but the pages are all blank. It worked just fine on the old
computer with win98, but won't work now with winXp sp2. I've tryied the
cartrdidges that worked before and new ones. The printer is USB
connected. Newest drivers are installed. I have followed the discussion
on this page, and tryied changing to 550c driver. It then faintly
printed half a sentence from a text document, and then the rest was
blank. strange!