I removed the cartridges, and noticed smudges where the black ink cartridge had been (the slot on the right).

Following Elward's suggestion, I unplugged the printer, shut down the computer, and waited 20 to 30 minutes. I then reconnected the hardware and rebooted my PC.

My printer started working again. Unfortunately, the print quality was as poor as ever.

I'll take the blame for the disastrous results of my first G&G Refill Kit foray. If I had been more patient, I probably wouldn't have had the splatter and leakage problems. Refilling more carefully the second time prevented most of that, but then my printer balked. In all cases, the output quality was subpar. If you want an inexpensive do-it-yourself refill kit for HP 60 cartridges, I have to say that the time I spent with the remains my best experience so far.