Problem with uploading files!

Hi,

I am using hostgator and have installed WordPress 4.0.

I have problems with uploading files.

For example, if I wan to upload a new theme or plugin, I go to “add-new” and then upload. I get the window with the following :
—-
If you have a theme in a .zip format, you may install it by uploading it here.
Below that text I see two fields for
Browse & Install Now

I click on Browse and find and select on my local PC the file I want to upload.

I then click on “Install Now”.

As soon as I click, the pathname that I had selected disappears and I never get to install anything.

I called the hosting company spend time time with them but they could not help me.

Does anyone know what the issue is?

Thank you in advance.