Unfortunately, there is no quick or easy fix here. This message indicates a hardware problem, specifically that that the internal "ink absorber system" is full. The ink absorber is a series of pads/tanks, which catch drips from the printhead when parked, and is also used for maintenance tasks like cleaning and purging.
Eventually this absorber fills up, and the printer shuts down operations, as continuing to operate it can result in ink overflowing the system, damaging your desk, flooring, etc
While it is sometimes possible to temporarily reset the counter (which is what you were able to do previously by pressing the stop or ok button) , this is dangerous as the system will likely overflow. This can only be done a limited number of times before the system truly is fully and can no longer be bypassed.
Cleaning/emptying/replacing the system is a difficult and messy process as well, best left to a qualified service technician. This service is generally not practical though - it's going to run you $150-250 for repairs, which just isn't worth it for an older printer. This is a 7 year old model, that was built for a service life of 3 years. If you have reached the point that the absorber has filled, then other wear items like the printhead, feed rollers, etc are also going to be at the end of their lives and need service/replacement soon.
Given the costs and complexity of fixing this issue, you'd be better off replacing the printer. You can get a brand new and better machine, with current technology and a fresh warranty, for about $80, which makes more sense than investing in the older machine.
I can recommend replacement options for you if you'd like, or if you'd prefer to try having it serviced or working on it yourself, I can advise further on those options. Replacement would be your best bet though, economically speaking.
Best regards, ***** ***** for the news,