Drush error cygintl-2.dll is missing
Apparently you have somehow broken your Cygwin installation. In the Cygwin setup.exe, go through the setup sequence until you get to the "Select Packages" screen, then type "intl" in the Search box. Open the Libs section, and click the third column on the "libintl2" line until it says Reinstall. Proceed.

That should fix this one particular problem, but chances are good that if you've lost that one library, you've broken other things, too. A complete Cygwin reinstallation might be in order.

You too can follow this steps for install drush properly:

Installing Drush on Windows 

or

Installing Drush on Windows using Cygwin