Install Webform on Drupal 8 : checkboxes greyed out (Pretty much a Drupal newbie here)

I'm having difficulty completing he installation of "Webform version '8.x-5.0-rc3 released 4 February 2018'" on Drupal 8.4.5 on a development box running Windows 10.

My Webforms installation is in my htdocs\modules\custom\contrib\webform folder, and 13 modules are showing up in Drupal admin/modules. But I can’t click on the checkboxes to install any of these modules because they’re grayed out. I’ve been able to intall other modules successfully, both homebuilt and contributed ones.

Any thoughts on how to proceed? Thanks in advance…..
The new webform 8.5 versions requires the "Contribute" module. If you click the little expander next to webform you'll see its a dependency. Have a look on the webform project page for more info 
https://www.drupal.org/project/webform

Also just as a tip as I noticed from your question you've got your modules as /custom/contrib/webform its better if you do your module file structure as:

/modules/custom/

/modules/contrib/

with your own build modules in custom and anything from drupal.org in contrib.