The free software Kubrick will reinstall a fresh 3.4 software. You'll need to update it to 3.4.2 after that.
https://www.mobileread.com/forums/sho...d.php?t=206064
The cover removal is a good suggestion if you have it in one of the Amazon leather unlighted covers. The clips which that one mounts with have been known to have the paint wear off causing problems with the kindle operation.