1. Re-install or update (Newest version is 3.1.3 BTW) your Electrum wallet, there's chance the application corrupted.
2. Check if another application working properly. If other application don't work properly, try to reinstall/repair your OS since important system files might be missing or corrupted.
Also, check whether your network status (in Electrum).
Thank you very much for all your advice.
Please confirm that this is how I should update:
1) go to electrum.org
2) download the latest file for OSX
3) run the dmg file
4) a popup opens with the electrum logo in it
5) drag the electrum logo into the Apps folder over the existing version I have installed
I think that this is what I did last time and everything was updated and all my wallets were accessible properly without having to restore anything from the seed.
Thanks
Go to file > save copy and make a backup of your wallet file just in case. Then update electrum like you did last time.