It sounds like there might be a server issue or a problem with your Magento installation. Here are a few things you could try to troubleshoot the issue:
Clear your cache: Clearing your cache could help resolve the issue. Go to System > Cache Management in your Magento admin panel and clear all caches.
Check file permissions: Make sure that the files you're trying to upload have the correct file permissions. You can check this by using an FTP client to log in to your server and checking the file permissions for the directory where the files are being uploaded.
Check server logs: Check your server logs for any error messages that might be related to the issue. This could help identify the root cause of the problem.
Disable extensions: If you have any extensions installed, try disabling them one by one to see if any of them are causing the problem.
Upgrade Magento: If you're running an older version of Magento, try upgrading to the latest version. This could help resolve any known issues related to file uploads.
If none of these solutions work, you may need to contact your web hosting provider or a Magento developer for further assistance.