... I'm afraid that a lot of the HP/Epson printers do this. It is a communication glitch. ALWAYS be highly sceptical of what anyone with PCWorld shirt on tells you. They are on low wages, that only become slightly reasonable if they sell lots. And then there are the ones that don't know what they're talking about...
(I once asked fro a min-VGA adapter and was asked what VGA stood for!
Anyhow, basically there are no quick fixes - yes, you can replace cables (never a bad idea anyway) but it will still happen even after re-installing the software, as you've discovered. It is a communication issue, however. The information coming from the computer is translated into ASCII characters.
When it happens, cancel the printing queue (all documents), as soon as you see the ASCII characters on the page switch the printer off - for at least 4 minutes. This clears the memory on both PC and printer. Switch printer back on and print the pritner's test page - all should be fine. Then resend your document to print.
There are some good printers available now. I have the Epson 880i which is great and although only a year old, has been superceded - but the good thing is it hardly ever produces the ASCII characters! Bought it for £199.
Cello