thanks for your post and welcome to Hello IOTA!
Both errors you've describes are most likely caused by being connected to a node that's out of sync.
Go to „Tools“ -> „Edit Node Configuration“ -> choose "Custom" in the dropdown menu and and put this into the empty field below: http://nodes.iota.fm:80
Then set Min Weight Magnitude to 14 and try CCurl Implementation first.
Click „Save“, close the wallet, restart it and log in with your seed.
Go to the „Receive“-tab and generate and attach as many addresses as you’ve used before the snapshot to make your correct balance show again.
If that still won’t work, change back from CCurl to Webgl 2 Curl Implementation. It depends on your system’s GPU/ CPU power which one will work better for you.
You can also check the address that should hold your funds on https://thetangle.org/
to see if your funds are still there. If you don't know which address that is, go check your withdrawal history on the exchange where you got your coins from. We can then track your funds together if you post your withdrawal address here.
I wouldn't be able to help anyone without thetangle.org-explorer. If you feel like you want to support its developer Mathieu Viossat in maintaining his service, please consider a donation to the address shown here: https://thetangle.org/about. Thank you!