If you provide a screenshot or any logs about what error you get when you upload your site, that would help us understand the issue and we can tell you exactly what to do.
That being said, there are a number of scenarios and solutions you can follow:
1. Re-Upload your files
Just upload your files again and select skip option for files already exist on the server. Make sure all files are uploaded correctly.
2. Upload via cPanel
A better option is to zip/compress your files and upload via cPanel File manager. Then extract the zipped files and you're good to go.
Some other situations to think of;
1. What about the database?
Did you upload the database from your old hosting/server to the new one? Make sure you do that.
2. Old and new site's URLs
The old website (domain) and the new site/domain, are these the same or different? If different then you need to replace URLs as well.
Change URLs by running this query in your database (use phpMyAdmin if you have cPanel)
UPDATE wp_options SET option_value = REPLACE(option_value, 'ORIGINAL_URL', 'NEW_URL');
UPDATE wp_postmeta SET meta_value = REPLACE(meta_value, 'ORIGINAL_URL', 'NEW_URL');
UPDATE wp_posts SET guid = REPLACE(guid, 'ORIGINAL_URL', 'NEW_URL');
UPDATE wp_posts SET post_content = REPLACE(post_content, 'ORIGINAL_URL', 'NEW_URL');
Source: WPBeginner