Site transferred but keeps reverting back to old installation

Hey guys,

So someone has transferred website files over for me to install on my host and I did it the best way I can trying to follow guides online. I installed the WordPress files and the database files and somehow managed to get them working, but I am having a strange problem.

While I’m in the dashboard updating the site and adding articles, it will suddenly log me out and take me to the admin login screen. The weird thing is that my login no longer works and the website goes back to the way it looked when the old owner owned it on his hosting account. All of the articles I wrote disappear and his old AdSense ads even come back up. After a while my new articles and edits show up again and my login works.

Any idea how to fix this, it’s been 2-3 days since transfer, could the domain nameservers be acting up and switching between my host and his? Any help would be appreciated, thanks!