If you're yahoo mail won't attach files, consider the following solutions:

1. Check your internet connection to ensure stability.

2. Confirm that the file size doesn't exceed the 25MB limit.

3. Make sure the file type isn't blocked or restricted by Yahoo Mail.

4. Clear your browser's cache, cookies, and history.

5. Temporarily disable browser extensions or add-ons that might interfere with Yahoo Mail.

6. Try using a different browser or device to attach the files.

7. If the issue persists, contact Yahoo support for further help.