I have the seed given when I first opened the account - would that be the one to use?
Yes.
And would that be restoring the wallet in the new version?
You can use the seed whenever you want to restore your wallet (regardless of the version). Since your wallet isn't (somehow) working, you can try restoring it while in the new version.
P.S: NEVER LOSE THIS BACKUP SEED! Without it, you can't restore your wallet if anything happens with it.