I have a HP c6100 all-in-one machine. The round

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)