welcome to Hello IOTA!
Without any further info, my first guess would be that the reason why your balance doesn’t show is probably that a snapshot deleted your transaction history and now the Lightwallet needs your help to „remember“ which address had your funds.
Let me start by saying that the Lightwallet is outdated and doesn’t get any updates anymore.
While it is still working, one issue is that the nodelist isn’t maintained anymore either, which makes it hard to find a working node.
That being said, if you want to keep using the Lightwallet regardless, you can try this:
Tools > Edit Node Configuration > Custom > put this in the empty field below: https://perma.iota.partners:443
Log in with your seed and if your balance isn’t back yet, go to the Receive tab and generate and attach as many addresses as you’ve used before.
The new Trinity wallet makes this snapshot transition a lot easier and you can just switch to Trinity by logging in with the same seed you’ve been using with the Lightwallet.
You can download Trinity wallet from here: https://github.com/iotaledger/trinity-wallet/releases
First go to Settings > Node, disable all options except "Use remote node list" and select this node from the dropdown list: https://perma.iota.partners:443
Then log in with your seed and make 1000% sure that it’s really the correct seed without any typos and such.
If you've noted the checksum of your seed at creation, pay attention and see if it matches.
If you can’t see your balance right away after login, go to Settings > Advanced Settings > Snapshot transition. You can also try a Manual Synch.
Let me know if you run into any problems.
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