Billing Details unwritable in IE

Which version of IE are you using? I just tested with IE10 and IE11 and had no problems.

Try switching themes to rule out an incompatibility.

I am using IE11 but also switching theme the situation does not change.

Do you have access to another PC to test? Does the same thing occur on https://demo.woothemes.com/ ?

Try inspecting the element to see if an iframe or anything else is blocking it https://msdn.microsoft.com/en-us/library/gg589507(v=vs.85).aspx