My account says that I don't have any games installed and I haven't bought anything. I uninstalled Never Winter Nights Diamond because it was crashing and I can't reinstall it now. Now it's asking me to buy the game, on my account settings it says I don't have any games in my library and I haven't made any orders. I haven't used this account in a year or two.

1. Contact the GOG support.

2. Are you 100% sure this is the same account where you bought your GOG games? Check your email account (the same email with which you logged into your GOG account), do you see the receipt emails from GOG when you purchased the games from them? They are your primary proof of purchase.

3. Related to point #2, you said you haven't used this account "for years", but it was created less than two years ago. So... did you create a new account back in Oct 2016, bought some games in it, and then instantly abandoned the account for two years? Did you install Neverwinter Nights back then in Oct 2016 but didn't use it since then, but had it installed on your PC all this time? Please elaborate.

4. Did you buy your GOG games straight from GOG, and not from shady key reseller sites like G2A etc.? If you bought GOG key codes from somewhere else, it is possible the codes were obtained originally in shady methods for which reason they've been later removed from your account.

5. No, really, contact the GOG support. I'm not joking, I am totally serious. This is my serious face. :-I

What happens when you access your account WITHOUT going through galaxy?

Try using this link, and see if you can access your games.
https://www.gog.com/account

your profile says zero as well.

this is odd.

I'll refer it back to point #3 from timppu's post.

I'm going to go ahead and point to 3 as well.