Flush DNS

Step 1: Open the Terminal
Navigate to Applications -> Utilities -> Terminal

Step 2: Flush DNS – Type the following command and hit enter.
Mac OS X Yosemite and later


sudo killall -HUP mDNSResponder

Mac OS X Yosemite v10.10 through v10.10.3

sudo discoveryutil mdnsflushcache

Mac OS X Mavericks, Mountain Lion and Lion

sudo killall -HUP mDNSResponder

Mac OS X Snow Leopard

sudo dscacheutil -flushcache