I have a HP Photosmart C6280 all-in-one printer, which is about 6 years old now. I don't use it very often but it occasionally comes up with an "Ink system failure" error message. I suspect this is because the print head is getting old and is failing intermittently.
Sometimes I can just reset the error message, which is usually "Oxc19a0007"
but it doesn't always work, The HP help pages are next to useless !
But I seem to have found a solution. The problem with these error messages is that they get "stuck" in the machine and need to be removed and reset, otherwise the printer just sits there and sulks for ever more.
So switching it on and off doesn't work, but I found this on the 'net this morning and its worked marvelously.
http://h30434.www3.hp.com/t5/Ink-Toner-Cartridge-Printhead-Issues/how-do-i-resolve-an-ink-system-failure-for-c6280-error/td-p/1117785
You need to get into the system reset on the printer, by pressing both Red Eye Removal and PRINT PHOTOS at the same time and go on from there.
Why HP don't tell you this is a mystery but I expect its because they want you to go over to Tesco and spend another £69 on a new printer !
The print head on my trusty C6280 will fail altogether at some time in the future but by following the advice in the above link, I still have £69 in my bank account this morning !