Hi I resently had a massive paper jam - after that was fixed the little catridges in the printer the black one we had to replace whe have replaced the catridge --when i want to print there is a green light flashing at the power button and i dont know what to do i have checked everything again Please help

SOURCE: Carrier Jam

This article gives a few suggestions on how to resolve the issue: http://support.lexmark.com/cgi-perl/knowledgebase.cgi?ccs=229:1:0:462:0:0&framed=&docid=ENUS24402&relevance=1

SOURCE: paper jam

Try this linke below.
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=110&prodSeriesId=411171&prodTypeId=18972&prodSeriesId=411171&objectID=c00642524

Or i cut and paste text, but you should view pictures. If you cannot get to it from link. Try typing "Paper jams alternating between front and back door" It should be first link from HP about a 3550.

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HP Color LaserJet 3500, 3550, and 3700 Series Printers - Paper Jams Alternating Between Front and Back Door Issue Description Customers may see paper jams error messages with no paper seen in the paper path. The message will alternate between check the front door and the back door. Workaround The release lever engagement tabs on the rear door can be bumped into the in-correct position. The purpose for this tab is to re-engage the fuser release levers as the rear door is closed. When one or both of these are left in the in-correct position the printer goes into a cycle of alternating between a "Jam in the Front Door" message and "Jam in the Rear Door" message. There is no paper present in the paper path when this happens. When a customer gets the "Jam in the Front Door" message and opens the front door, no paper is found. After the customer closes the front door, they get the "Jam in the Rear Door" message. When they open the rear door, find not paper (even pull out the fuser), and close the rear door, they get the "Jam in the Front Door" message. This cycle will continue

Placing both engagement tabs in the "Correct" position solves the problem and allows the print job to continue.for as long as the customer is willing to keep checking.

SOURCE: I have a xerox phaser 3124 which have a paper jam

Xerox printers have known issues with the rollers. You may want to look into getting some new rollers, they're not that expensive. I think with this model there's one in the tray, and one up above where the paper enters the printer.

SOURCE: printer indicates catridge error

we need to perform a reset, it will take the pritner to the factory settings and this may help you,
the process of reset goes like.
unplug the power cable from the pritner >
then press and hold down the # key and 6 key >
while pressing and holding these keys plug in the power cable back into the printer and wait for 20 secs and then release the buttons..
after this the printer will re-initialize and this might take few minutes.. so wait untill it finishes and follow the onscreeen instruction as well.(if any)

SOURCE: I replaced the blue catridge and now both red

If the red lights are flashing simultaneously, it means that there is something blocking the printhead from moving. check if all inks are installed properly and the ink carriage cover is closed tight. If both red lights are flashing alternately,it means that the waste ink pad is full and needs to be replaced. This part is not user replaceable so you need to take in the printer for service.