Printing Errors or Lights & Stuck Print Jobs

 Our office jet pro 8600 plus suddenly stated "there is problem with the printer or ink system" error message.  It was already on and had printed fine just the day before. Only had the printer 4 years & keep it exceptionally clean (no children around).   We use it periodically every week or two...still looks new.  We've always only used brand new HP ink cartridges and replaced them when the printer indicated they needed replacing, so why is this happening?

   I have followed the HP online troubleshooting guide (including buying new HP cartridges), but nothing works.  I checked/cleaned the internal areas, including removing/cleaning the printhead area per HP... stil same error.   I tried some of the suggestions online (including Youtube)... still same errors. I did try resetting the CMOS battery only for the purpose of erasing memory of the ink system error message hoping it would reset but that didn't do any good either (CMOS battery does not need replacement at this time). Now I sometimes also get a "printhead is missing or installed incorrectly" message, even though it is reinstalled correctly. This is ridiculous! 

   I hope HP or someone else has a workable solution. Replacement printheads are ridiculously expensive.  It's so out of the blue it seems like it's caused by an HP update. Had a similar problem 6 mos ago when it would print only part of a page. Couldn't figure out what was wrong, gave up and bought a new printer but before I took that out of its box an HP update fixed the issue. I have several ink cartridges still that can't be returned to the store so they're wasted. If I have to buy another printer, it won't be an HP one, that's for sure! So if HP wants me to continue using HP products, please help!