I suggest google for  'Sys is not defined'

research and solve that problem, once it is fixed the other error about Get_Cookie may also be fixed as it may be caused by that one

I tried to look at your site but it currently does not show the page so I cannot try to diagnose it further.

I would make sure you are using .NET 4.5 and have all the windows updates installed, possibly something is messed up with the installation of .NET framework on the server.

I would try different skins to see if it makes any difference.

Google for "scriptresource.axd not found" you will find lots of information about this and possible things to try.

one thing you could try is creating an empty text file in the root of the site named scriptresource.axd becuase it seems like IIS is returning a 404 without giving .NET a chance to handle the request, by putting a fake file there it may prevent IIS from returning a 404 and give  .NET a chance to handle the request 

I would try re-installing .NET framework on the server, something is wrong with your .NET installation

Glad you got it sorted out, some days technology can be a real struggle but you struggled through and prevailed in the end.

Still think there must be something not quite right with your .NET installation since this should not be needed in Web.config. I'm pretty sure stuff like that is supposed to be in machine.config in .NET 4 so it isn't typically needed in web.config. This was one of the changes in .NET 4 whereas back in .NET 3.5 we had to have those things in web.config, in .NET 4 they moved that stuff to machine.config and we cannot usually have it in Web.config because it causes an error if it is in both places. So your machine seems to somehow not have that in machine.config.

I think sometimes things go wrong when .NET is installed before IIS is installed, sometimes not everything gets wired up correctly when IIS is added later. If IIS is installed first then things usually get wired up correctly for ASP.NET by the .NET installation but if done the other way it doesn't always. Anyway that is one theory of how some machines don't work as expected for ASP.NET.