Replaced drum. still won't print. says replace drum! help!

The problem occured right after you replaced the drum ?
You could have a defective drum module, but I would suspect that when you replaced the module and turned the orange handle the developer housing did not cam in properly.
You can remove the left cover and push the developer housing in toward the drum.
Sounds to me like the housing just did not return to the home position.

sir/mam drum do go bad after so many copies and prints. normally machine will indicate when that is needed.

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/normanj_7893313f0751935f

take all paper out. check to see if any paper is jammed in the rollers
go to application folder for your computer, dbl click icon for make of printer, for settings, check to ensure everything is order.
lastly, check make of printer trouble shooting web site for more information
hope this helps, good luck.

Open the front door, and press the go button until the lights flash, after closing, press the go button 3 times for a printout showing the drum as full again. The instructions come with the new drum...

Replace the toner cartridge.

If all the colors are effected by grainy look, then it could be the imaging unit like you were told or the transfer belt. Unfortunately there generally isn't a way to test which one it is but to swap and test.
If you are still having issues, check out www.killmyprinter.com

Replaced black toner when the machine told me to, then replace drum when it told me to. Now it won't do what I tell it to!! I am getting ghost print on everything, can't find solution in the HP manual so if anyone has any suggestions I would be very grateful for your advice.

Ghosting can :
1-prints on the fuser roller, check if yes try cleaning it off, wait until it cools off

2-blanking lamps dirty or not working,(deletes image off the drum, before it gets ready to accept a new one)

BL mirror-(new image)
\ /
()
drum

3-Bad drum (although I doubt it this far in the process.)

Have you replaced the printer drums? The status monitor will tell you what percent they are at (similar to the toner cartridge status). This fixed my problem before.

Your almost there. Now you need to replace the 'Transfer Roller'. The transfer roller transfers the image from the drum onto the paper. If this roller is worn out all you'll get is blank pages printing out. Ray CompuGuy44