Hello Judy,
Does your 4640X eventually land on the Recovery Mode screen?
If not, you may have a different issue. Search the Roku Community site for your specific issue. If you're unable to find the specific issue with your player start a new post.
If your 4640X player is displaying the Recovery Mode page and you're not able to recover after attempting to update, then restart, and then factory reset, a Roku Community Moderator should be contacting you via PM. If you do recovery use please update this comment so the moderator knows your issue is resolved or unrelated.
If this was an update issue and Roku is working on a fix, it is possible for Roku to send out an update. From the recovery mode screen we can connect our players to Wi-Fi/Ethernet in order to update our players. Therefore if Roku does manage to fix/patch the issue affecting 4640X players it may be possible for us to recover use of our 4640X Roku Ultra devices.
Good luck.
Cheers!