Eson 740 will no longer print black ink

The printer has worked great for 6 years and now it stopped printing black. The color ink works fine. The blinking light to indicate "out of ink" never goes on. I have changed the black cartridge "3" times with no success. Once I got it to print black when I changed the printer features to "Resolution: 1440 x 720 DPI Highest Quality." However, after 3 pages, the black began to fade again.

About drivers: When I ran this on OS 9, there were drivers. But on OS 10.3.9, you use the System Preferences and simply chose Epson 740 from the menu. So I am not sure if the driver is the problem or even how to re-install the driver. Any help would be appreciated. Thx.