Most probably any of your Installed Plugin is responsible for this. Please deactivate all of your plugins and activate one by one to find the problematic one. Sometimes, the server resources may not be sufficient for WordPress. You can read This Article.
You can try the FTP Method of Installing Theme.
You can alternatively provide us the Site URL, One Temporary Admin ID and Password and FTP Login information to this E-Mail: [email protected]
Thus we can check your issue. But, we are confirming you that is not a Theme Issue.