In 2010, you came across a site that was giving away bitcoins. The site said it was free money so you signed up. You were logging in to figure out how it was money but couldn't. The last time you logged in you had more than 100 bitcoins. Later you forgot about the site until 2017 when a ponzi was advertising Bitcoin. Bitcoin? The name rang a bell and you stated hearing stories. You remembered you must have many bitcoins somewhere but you can't even remember the name of the site. How would you recover your BTC?
That's seven long years later. There will be a lot of questions here. Have you not heard of Bitcoin from that particular moment on? Did you not hear even one particular news about Bitcoin in 2016 or even in 2015? Bitcoin was already popular during those years. Where were you back then? If the site is still in existence until now, try to recover your account. And then you will take the next steps from there.