There are gaps,skipping lines, even printing the top half of a line then a gap, then the bottom half

This sounds like your word program and not your printer. The information from your word program is not being sent from the DLL correctly. Try a different word program or try reinstalling word.
Phill

Reload the printer drivers, you can get this from the manufacturers web site under support or downloads.
its a common error and an easy fix.
good luck !

it seems that the print head is clogged try printing the nozzle check if ok change the black cartiage .

Follow these steps to print a nozzle check:

1. Turn off the Epson Stylus dX.
   
2. Disconnect any connected USB cables.
   
3. Load letter-size paper in the sheet feeder

Hold down the Stop button as you press the On button to turn the Epson Stylus CX back on. Hold down both buttons until the On light begins to flash, then release the buttons.Tell me the result-->Nozzle check pattern with no gaps or with gaps?
You can use this service/repair manual for Epson dx7400 ->start download.

Here is a full detailed explanation on how you can avoid Epson printer skipping lines

https://www.errorsdoc.com/epson/how-to-fix-epson-printer-printing-with-lines-missing-or-printer-skipping-lines-issues/

Label definition in printer driver may need adjustment. Try calibrating printer, printer on solid green light, hold down feed key & release after light blinks 4 times, (blinks once, twice, three times then 4 times) Download the Zebra setup utility and use it to configure printer.

try to do a system restore to a date when it was working ok, if still no go, then reinstall the printer driver.

If you try the print head alignment or head cleaning wizard under the maintenance tab, they may help!

White Lines on the Printed Page ID:193
Clean the print nozzles as follows:

1. Go to Start, Programs, Lexmark, Lexmark Solution Center (or Lexmark Control Program) and select the Cartridges tab.
2. Select Cartridge Nozzles (or Clean Print Nozzles).
3. Check the diagonal lines above and below the solid horizontal lines. The diagonal lines should be continuously solid from left to right, with no gaps.
4. If there are gaps at the top that diminish at the bottom, run the Clean Print Nozzle page a few more times. If the gaps are gone, the Clean Print Nozzle page has probably resolved the problem.
5. If the gaps still exist, you should unblock ("wick") the cartridges. See How to Unblock/Wick the Cartridge Nozzles.
   For additional help, refer to the following article: How to Clean the Maintenance Station .

Hey Danzo, This error is usually caused by dirt (usually toner) on the laser lens. There should be a cleaner pad somewhere on your machine (though I am not totally familiar with Oki) that will wipe across the lens. If there is no pad, you may have to find access to the lens and wipe it manually with a tissue or similar