Thank you SO much for your help. I've actually come up with a reason/solution which might be worth adding into any support material - the bits where it says about troubleshooting and file types? This is obviously me, a non techy talking, but maybe it can be translated into proper language!
So I found out there are different types of MP4s? HD, VGA, SD, HQVGA and one which I've got here as 'low' whatever any of that means. If you save your MP4 as 'low' it works in ES. I presume this relates to file sizes or some such and the rest are too big for ES? I probably sound really thick putting this here and everyone is saying, "Duh, didn't you know that?" :-)
Anyway I'm happy typing my captions, marking shot changes again and being to ID speakers as I transcribe my audio. :-)
Thanks again for your support and help. I love ES and no matter what anyone tells me about FTW transcription stuff, I'm sticking with it (as I have since 2009!) It would be good though if you could calibrate time stamps to video clips, as in if a video has an embedded time code and you want want ES time stamps to match that... For Christmas maybe!
Maz