You first want to make sure you still own and control your domain name by logging into your domain name registrar account, where you bought the domain name, and making sure your DNS settings are correctly pointing to your web hosting account, where your web pages are located.
Continue and make sure all of your contact information for the domain name is correct. Then change your password for both your domain name account and also your web hosting account. If you can turn on 2FA, do it for both accounts.
If you use Google’s Search Console, and you should be, you can add your ownership to your domain name by adding a TXT record via your domain name account, verifying it, and then checking other relevant information from the console.
And as a last resort, clean your browser’s temporary files and reset your browser’s setting. Also, run a full antivirus scan on your system.