Unable to install plugin from 'Pluings>>Add New'. Showing error message

Dear WordPress Developers,

Recently I installed WordPress 4.3 on my server. But unfortunately I am unable to install any plugin from ‘Plugins>>Add New” option. If I search any plugin and then if I lick on ‘Install’ button of any plugin then wordpess showing the following error message:

“Problem with the SSL CA cert (path? access rights?)“

Please read the issues below with screenshots. I am receiving this error at the following areas…..

1. At ”Wordpress Dasbord>>Wordpress News” at the RSS News field. See screenshot: https://www.dropbox.com/s/g7e3ozgdnlm498h/Wordpress%20News%20Error.png?dl=0

2. At WordPress Dashboard>>Plugins>>Add New unable to install ANY plugins. See screenshot: https://www.dropbox.com/s/tp259eexk5lsu5v/Plugin%20Installation%20problem.jpg?dl=0

3. Inside of some plugins.
When configuring or making authentication or making cloud backup is not possible. See some of plugins screenshot below:

– Error in ‘Updraftplus backup plugin’ for dropbox or google drive cloud backup: https://www.dropbox.com/s/xer87ilg8rqm2tf/Updraftplus%20backup%20plugin%20backup%20error.jpg?dl=0

– Error in ‘Backwpup’ for dropbox cloud backup: https://www.dropbox.com/s/lu789r9wpoaxz9z/Backwpup%20error.jpg?dl=0

4. While attempting to update any plugin. https://www.dropbox.com/s/fd2f0qlhpx5jmpp/Update%20plugin%20error.jpg?dl=0

5. Feeling site is loading slowly. There are may be something making the site slower.

Please kindly let me know what the issue is going on wordpress. And please tell me how can I fix it?
Thanks