i have 2 copies of my wordpress website one online and the other offline the code now is working on offline but on the online some scripts stopped appeared when i used contact 7 plugin but i fixed it but now when i activate it online i website crash but offile every thing is working fine is that means someone is hacking my site or there is other problem the problem
Are you using different versions of WordPress in the 2 locations? Are there any other plugins that are different? Perhaps the PHP setups are different between local and online. There's lots of things that could be different other than the code.
Personally I would recommend the Jetpack plugin (http://jetpack.me/) and it's contact form extension. I like that it's made by the wordpress.com team since you know they'll make something powerful and constantly maintain. Plus it's surprisingly flexible :)