I was found the titled problem when I was first time installed Magento version 2. But, if you follow bellow steps hope the issue will be resolved.
Step 1: Run CMD [click windows start button and type ‘cmd’ and click ‘Command Prompt’]
Step 2: Goto Magento installation directory using ‘CD Magento directory full path’. [my directory was ‘D:\xampp\htdocs\magento’ so I was typed ‘CD D:\xampp\htdocs\magento’]
Step 3 : Run ‘php bin/magento setup:static-content:deploy’. Sometimes we need forcedly to do this so type ‘-f’ and press ENTER button.
Step 4 : Run ‘php bin/magento indexer:reindex’
Step 5 : Delete ‘cache’ from ‘var/cache/’ [delete all folders under cache]
Enjoy! It’s getting work for all Front-end & Back-end!!
If anything else please doesn’t forget to knock me!!!