WP Plugin update errors

This seems to be across two different WP Installed sites site so far - not tested the others but I have two issues at present.

1. Trying to update existing plugins i get

Download failed. Couldn't resolve host 'downloads.wordpress.org'

This happens on all the plugins I try to update? Due to this I am reluctant to update WP to 4.0.1

2. Reinstall buddypress
Buddypress disappeared after WP auto updated on a different site, it doesn't appear in plugin list but the folder does exist on server, so I deleted it to avoid 'already installed' message and tried to reinstall, however it simply stalls at either

'Installing.....'

or

'Unpacking...'

After a few minutes I notice it does creates the folder again in the plugin DIR, but not list it in plugin list so can't activate etc?

Any ideas?

Edited November 28, 201411 yr by DaveyL