HP 3550 printer: copies are coming out with faint images of previous printing jobs

Have you calibrated your printer after changing ink cartridges?

Check ink-levels -- no ink means no printing.
Run a few more "print-head-cleaning" cycles -- clogged ink-jets cannot spray ink onto the paper.

1) try doing a full clean from within the menu on the printer, or within the computer software
2) You need to perform a half test. Put a sheet of paper on the manual feeder and do a config page from the information menu on the printer. When the back edge of the paper enters the printer, quickly open the toner door to stop the printing. Now remove the toner cartridge and look at the image below. If the defect is present, then the toner cartridge is the problem 99% of the time. There is a slight possibility that during the conditioning stage of the print process the drum of the toner is not being fully discharged so when the next stage takes places part of the previous image gets put on the toner cartridge again. Very rare. If the defect is not present then the fuser has an issue.

restore the properties.... set as "print in grey scale" or "print color as b/w images"...
also if the print become less or more dark you can change the settings to print whit more intensity or less...
there is no necesary change all your documents as "watter ink" only change the print options to fade to black

try performing a hard reset by holding go and turning on the printer.....otherwise you may try to download the current firmware from hp and install...

my printer did not take the printing job. I wnt to cancel the job but it is not cancell lsat one job is still pending. If acctionally take the print firt two line is printing the rest of the matter is pending and that job is not able to cancel . I have hp diagnostic utility but it is also not working to release the printing que. kindly do needful to solve this problem

Time for a new drum unit

I can tell you that it is NOT the Fuser unit. I would change the drum unit first. This would be the most likely cause.

Depending on how many copies you have run, the drum as well as the cleaning blade needs to be replaced.  That should get rid of the gray band.

You should remove the printer driver and reinstall the printer driver. If that does not help consider re-installing windows. And if the same occurs again, get help from HP service at your area. or you can get support from the manufacturer's website.