On my canon lbp 2900 printer it shows no toner cartridge open the top cover and insert a toner cartridge, i did that several times but the problem remains the same, help me out.

maybe is a maintenance issue

Had the same problem. This is what worked for me:
Switch off the printer, remove the power cable, remove the usb cable, wait for 10-15 seconds. Re-insert the cables, switch on the printer. Mine worked after that.

Note: Need to clean the printer after replacing the toner cartridge. Only use the toner cartridge designed for this printer. NEVER touch any of the high voltage parts inside the top cover. It will damage the printer.

^ Open the top- Grasp the groove on the right side of the top cover and open the cover until it stops.
^ Lift the toner cartridge in the direction of the arrows then pull it out
^ Take the new toner cartridge out of the protective bag -- as there is a notch cut into the protective bag near the arrow, you can tear open the bag by hand. However, if you are unable to tear open the bag by hand, you should use scissor to cut the bag open to avoid damaging the toner cartridge.
^ Hold the toner cartridge and roll it gently from side to side 5 to 6 times to evenly distribute the toner inside
^ Place the toner on a flat surface, then slowly pull out the sealing tape(approx 50 in length) while supporting the toner cartridge.

For complete instructions: http://support-my.canon-asia.com/contents/MY/EN/0900670504.html

Did you make sure that the new toner cartridge doesn't have a orange pull tab on the side. If that is left in it will make the toner not recognized by the printer.

See the following website for illustrated instructions on to replace your toner cartrdge.

How to replace the toner cartridge

http://support-in.canon-asia.com/contents/IN/EN/8000596401.html

Trust this is helpful.

It is very easy to open the printer.First you need to remove the screws at the back.Then slowly remove the white panels which is fixed at the left and right sides.You should be very careful doing so,because there is no screws instead of that only plastic locks.Then you can remove the top cover.The total plastic panel you can remove only removing the two screws.Best of luck

I recommend you do not try refilling toner cartridges, the toner powder is very fine and you do not want to breath in this toner powder.
You can purchase a new toner cartridge or a cheaper alternative is a re-manufactured toner cartridge.

open the top cover and insert a toner cartrige

same problem!

I have a same problem .... somebody help us. :(