When user unable to register my Digital Signature Certificate or DSC, or While trying to e-file Income Tax Return using Digital Signature Certificate of DSC, the "Select Your .pfx file" or " Select with your USB Token" button are not selected or displayed or are not clickable.

Step-1: In this case, uninstall all the version of Java and install the latest version of JAVA from JAVA WEBSITE.
Further, add domain of website on which Digital Signature is used in the exception list of site in Security Section of Java.

Step-2: Enable all the options of Active-X Controls and plug-ins

Internet Explorer >> Tools >> Internet Options >> Security >> Custom Level >> ActiveX Controls and Plug-ins