It seems that you decided to connect your PC/Laptop to the internet and let your wallet sync.

If the funds or your balance become 0 after syncing there is a big possibility someone already has access to your wallet(Or you might be infected) and sent it to another address. In that case, you can't able to recover them because Bitcoin transaction is irreversible.

If you talking about "it syncing after a few blocks are downloaded the transaction history gone?"
It could be a bug if the wallet was started in 2009 and 2010 and has never been touched until you open the wallet and after syncing the wallet transaction under history is gone it could be a bug.

What I would like you to do is to get all used addresses under your wallet(If you can able to check the addresses tab) and check them one by one in the block explorer. If all addresses from your wallet do not have funds and one of your addresses has one transaction under history then it was already sent to someone and possible someone has access to your wallet or your PC is infected and you can't able to recover them.