Thanks webprods, I really appreciate your help 
Though it all started working before I even needed to follow the steps in your last message. I don't know what changed... but suddenly it works!!
I do have another slight problem now though
I think I forgot to copy the correct wallet.dat into the Roaming folder (d'oh... I was distracted by multiple attempts to get it to sync), and I'm not seeing the transaction from Bittrex on 7th April. Bittrex support say they can't do anything since it's already classed as completed. I transferred a small amount which worked fine (and very quickly!) - was hoping that might trigger the old transfer into working but no joy.
Will it just catch up sometime? Or has my stupidity resulted in me losing those XCO forever?
EDIT - if I delete "blk0001.dat" and sync from the beginning again, would that work?
Though it all started working before I even needed to follow the steps in your last message. I don't know what changed... but suddenly it works!!I do have another slight problem now though
I think I forgot to copy the correct wallet.dat into the Roaming folder (d'oh... I was distracted by multiple attempts to get it to sync), and I'm not seeing the transaction from Bittrex on 7th April. Bittrex support say they can't do anything since it's already classed as completed. I transferred a small amount which worked fine (and very quickly!) - was hoping that might trigger the old transfer into working but no joy. Will it just catch up sometime? Or has my stupidity resulted in me losing those XCO forever?
EDIT - if I delete "blk0001.dat" and sync from the beginning again, would that work?
Yes, you will have to redownload the block chain. Tell us how many you were supposed to have if you can't get them to show check the block chain to double check.
If not just post them amount I might have enough to cover some if not all. You better be using the faucet.
