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Parallel-to-USB adapters can be flakey / unreliable. I would advise you to reinstall the driver for the adapter, if you are printing from a POS terminal with an operating system on it that can have drivers installed on it.
If on the other hand you are printing from a basic cash register's parallel port, then I would advise you (given you have done everything else) to replace the parallel-to-USB adapter after re-seating both sides of the connection and making sure it is well and firmly seated at both ends, with the power Off on both printer and register of course.
If your 'register' is really a PC, please tell me what Windows version is on it.
And, let me know if you've made any progress with it.
My sense at this point is that either the old printer or the (unreliable?) parallel-to-USB adapter may be defective.
Did you ever (as what you quoted mentioned) plug the printer in to the computer before installing the driver again? if you did, that *is* confirmedly a mistake.
I think you say that another printer also does not work on this parallel-to-USB adapter ? then the adapter is more likely to be the problem.
If the computer has a USB port, I'd really love to solve the problem for you, by telling you to get an up-to-date printer that has a USB port and doesn't need the adapter (so if it's broken, that way it doesn't need replacing)... a printer that basically is guaranteed to work with your computer without extensive try-and-try-again and disk-imaging and so forth, which (if your time is of value) is really costing a lot. Printers don't cost a lot these days, it's the ink that really gets into your pocket money, so replacing the printer may be more efficient than you would think at first.
What are the current port settings there, for the printer and/or adapter, please?
IF there's an alternative to 'USB port' that references the USB-to-parallel adapter, you might want to choose that as the output 'port' instead.
USB Virtual, I would try. If that doesn't work and you have the patience to disconnect the printer, uninstall the printer, restart, and re-install the printer, choose Parallel the next time. ? just to touch all the bases on possible settings and choices, before concluding you tried everything.