Hi try this procedure, it works for my hp2500n:
I have to disagree with the below.
NVRAM reset does reset the HP2500's concept of number of pages,
but does NOT touch the count on the drum nor the color cartridges.
And it does not set override out. I believe there is no such setting
on the HP 2500 and the machine will BY DEFAULT continue printing
after the tone goes low. The light will go on steady when toner goes low, and will blink when 'empty' I am not sure if it will print beyond the empty point though.
To perform a NVRAM init:
1) Turn the printer off.
2) Press and hold the GO button (Green Button).
3) Turn the printer on and continue to hold the GO button (Green Button).
4) After the Go, Ready, and Attention LEDs turn on, continue holding for at least 20 seconds. During this process, the Attention, Ready, and Go LEDs will each turn off.
5) Release the GO button (Green Button).
6) The device LEDs will begin cycling from front to back. The NVRAM-init process runs until the printer is in the Ready state.
I found the info in a service manual PDF file.
I think it resets the toner counts and drum counts and you may have to reinstall the print drivers.
Hope this helps.