Hello lovelysidhu and welcome to the forum.
I am sorry to hear about the problems you are running into.
-- has the ST4 plug-in ever been OK?
-- VSTi or VST3i edition?
-- any error messages, dump summaries?
-- does the ST4 standalone program crash on exit?
As this is primarily a user to user forum, someone-else may chime in. Meanwhile, the best thing to do is raise a Support Ticket, here:
http://www.ikmultimedia.com/contact-support/mi/for some one to one help (US (East Coast) Business hours, generally). But they will want details.