When you say "copied" Wordpress, what do you mean?
Do you mean,
A) I copied my entire Wordpress installation folder to my new server location?
B) I copied ONLY my custom theme folder to my new server location?
If your answer is A then we can assume you did not install a fresh copy of Wordpress on your server before migrating.
If your answer is B then we can assume you already installed a fresh copy of Wordpress before migrating your theme.
B is the correct method unless you are using a specially designed migration plugin that helps you move your installation from location to location. Or unless you know how to manually work with your SQL file while ensuring to update any relevant URLs within that need changing to match the new destination.
If not, then the URLs that tell Wordpress where to expect certain areas like the admin dashboard, might still be pointing to your previous location.
Try adding the following lines to your functions.php file,
Replace the URL above with your current site URL. Save the file. Then revisit your login page. If it does not show up, refresh it a couple times. If it then shows up, we know this was the problem. You can now login to your site.
Once logged in, remove the entries in your functions.php file that you placed earlier. Then goto
settings -> general and make sure the URLs you see for site/home address match what you entered manually into functions.php before! It should match. But check it anyway to make sure.