Can't refresh data from spreadsheet

I've got a small dashboard (one page) which is linked to a data spreadsheet with about 4000 rows. I've added another 2000 rows to the spreadsheet but when I try and refresh the dashboard it just hangs and won't update -  I get the refresh window then it gets to 293KB and just hangs with the dots going round. I've left it overnight, it was still on 293KB in the morning. I've also tried rebooting/restarting/turning off AutoDate/time. Any other suggestions? I really don't want to have to remake the dashboard!