WordPress web site stopped working

I developed my first website using WordPress. Once it was working perfectly, I decided to create another website using WordPress too. The first website stopped working after I created the second. It looks like the second one erased my first website – whenever I go to the admin url of wordpress for the first site, it opens the second one. Unfortunately, I didn’t back up any data from the first website. I think the issue has come about because I installed both sites using the same database.
Do I need to rebuild my first site? How can I make them work using just one database?
