Ok I have copied the wallet dat, now do I reinstall the wallet and then copy the wallet.dat into the reinstalled wallet?
The wallet opened, but I have no coins in it now

how do I get them back? I still have old copies of my wallet.dat
I can unlock the wallet with my old key, I assume it has none in as it has not synced yet? I will wait and see if when it syncs my coins return, thanks to everyone who helped!