the HP LaserJet 2100, 2100n, and 2100tn Printers with firmware v 19991018 or higher can cold reset the HP Jetdirect using this method: Hold down the small JOB CANCEL button. Turn the printer on; continue to hold the JOB CANCEL button for seven to ten seconds, then release. Do not hold the JOB CANCEL button longer than 10 seconds. Printers with older firmware can cold reset the HP Jetdirect; however, the page count and serial number on the printer’s Configuration page will be lost (the serial number is, however, also printed on the back of the HP LaserJet 2100 printer).

This procedure is for reference only and should be avoided if possible. Print a Configuration page. This will ensure that a hardcopy of the current page count and the electronic serial number is available. Turn off the HP LaserJet 2100 printer. After the power is off, press and hold JOB CANCEL.
Turn the power on, and continue to hold JOB CANCEL until all of the LEDs come on or for five to 20 or more seconds after all of the LEDs come on.

How to Reset the Maintenance Page Count the HP LaserJet 4000 ,4050, 4100 Printers
When you replace new the printer maintenance kit will reset the maintenance page count.

NOTE: The printer will not reset the maintenance counter back to 0 until it reaches 200,000 pages.

To reset the maintenance page count the HP LaserJet 4000,4050,4100 Printers:

1. Press and hold down the left side of the ITEM and VALUE buttons on the control panel while turning the printer on. (The printer will not reset properly if the ITEM and VALUE buttons are held down on the right
   side.)
2. RESET MAINT COUNT appears in the display, followed by INITIALIZING.
3. After a few seconds, READY will appear in the display. At this point, the printer’s maintenance count has been reset.