Search plugin form on “Add Plugin” page not working

is this a localhost install of wordpress?

i had this problem with a localhost install, and it ended up being read/write permission issues between my /var/html/ folder and WP itself, and then it was read/write issues with the database :/

after working on it for a long time, i finally gave up and followed a different tutorial for installing LAMP/WP in one long step. and that fixed it.

if running WP on a VM for developement, first check to make sure your VM has network access. that occasionally breaks my localhost install.

good luck!