amicable wrote:video files all under 1.4 gb...they transfer onto card ok but after about 5gb they not recogniseable as video files and are unplayable
If you are confident that the video files are 100%-A-OK before transfer but no good after transfer then it sounds like a problem with the SD card. If any of these files are HD video then it is best to use a class 10 SD card otherwise you can encounter issues when trying to play video files.
Many cheap unbranded SD cards are not what the seller claims, there are many cases of class 4 cards being sold as class 10 cards when they are not, also some very cheap SD cards are not the claimed capacity even when registering as a larger size when installed they can be spoofed using a smaller capacity card.
Maybe none of these reasons apply to your card but it still sounds like a card problem if files are OK on a desktop PC.