When i put a dvd in my hitachi htdk185uk it says unknown disc what does this mean
Either a DVD with the wrong region code has been loaded, and your player doesn't recognise it, or you have inserted a disc which is either rewritable (or an incompatible format for your player), a blank DVD or CD, or the disc has not been finalised in a DVD recorder. It depends on the disc(s) you have, whether they are region coded or those using a compatible playback format (finalised DVD-Rs are the best as far as burned copies go).
Examples of incompatible formats for your player may include;
DVD-RAMs (which are the wrong version/speed for your unit)
DVDs with a different region code to your player or rewritable discs
* When using shop-bought DVDs, including those purchased online, make sure their region code matches your player.