.Net project not working well in certain browsers

I am working on a .Net 4.0 application, which works perfectly fine on IE8. However, when I run it on IE11 or chrome, it starts behaving wierdly.

I have used AjaxPro and javascripts extensively in my project. This is the main reason for the failure.

Could you guide me on how to handle this? Do I have to rewrite the entire code?