Sitecore Project - Localhost just hangs

I've been using this same Sitecore project, for more than 2 years now. Upgraded to Sitecore 7.0 this spring, and everything just ran like it should.

But yesterday, suddenly out of nowhere, i can't seem to run my project anymore. I'm using Visual Studio 2013 with IIS Express (64 bit). And when i try to build and run my site through localhost, it just hangs. I even tried to let it load for 1 hour+, but it still just loads with nothing happening.

I tried to debug it further with Fiddler, but nothing happens. I even tried to delete a bunch of important files, like web.config. But it still just loads forever, with no error.

If i create a new empty web project, i can start it through localhost instantly. So there must be something weird happening with my Sitecore project.

Does anyone have any suggestions for debugging this or have you ever experienced anything like it?

I've nearly tried anything.

I am not sure what version you upgraded from, but I would do the following (in order) to troubleshoot the issue:

Depending on what version you are upgrading from, you may have been running your app pool on .NET Framework v2.0 instead of v4.0, which is required for Sitecore 7. Open up IIS, go to your app pool for the site and make sure that it is correctly set to run on .NET v4.0 and not v2.0. If it was set to v2.0, change it to v4.0 and try access the site. If the issue persists or if the app pool was already running on v4.0 continue to the next step.
As implied in step 1, Sitecore 7 runs on .NET 4.5. If you are upgrading from an earlier version of Sitecore, it is possible that your site is compiled using an earlier version of .NET. Right click on your project files in Visual Studio, click on Properties->Application and make sure that the Target Framework for each of the projects is set to .NET Framework 4.5. If they were set to a different framework, change them, build your solution again, and then try to access your site. If they were already set to target .NET 4.5 or if the issue persists continue to the next step.
Double check the permissions on your site root. Make sure that NETWORK SERVICE and/or your IIS User has all of the necessary read and write permissions for the directory. If they do not, apply the permissions and try the site again. If the problem persists, continue to the next step.
Delete all of the Sitecore DLLs and the DLLs generated by your projects. Copy fresh DLLs from a clean download of Sitecore 7 back into your bin/reference directory and build your solution again. Try to access the site again. If the issue persists, then the problem is likely in temporary internet files or in a config. Continue to the next step if this is the case.
Delete your Temporary ASP.NET Files from the Framework and Framework64 folders found in the C:\Windows\Microsoft.NET directory. Note that you must go into the directory for the version of .NET that your app pool is running against and delete the contents of the Temporary ASP.NET Files directories. It may be necessary to stop your app pool when you do this. Try to access your site again and if the issue persists, move onto the next step.
Try replacing your web.config with the default from a clean download of Sitecore 7, but be sure to back yours up before-hand so that you do not lose customizations, as you will want to add them back in after. Try your site again. This time, you may get an error if something in your code is dependent on the web.config. It is a good thing if this happens, as it means that your site is now working and you have only to add back in your customizations to resolve the errors. If your issue persists, continue to step 7.
If your site is still hanging, try replacing all of your configs in the App_Config directory, one at a time, with their clean copies (excluding ConnectionStrings.config and DataFolder.config, if you are using them). Additionally, disable/backup and remove all custom configs or configs for modules that you have installed that are not Core to Sitecore. Try to access your site again. If necessary, resolve any config errors by merging your changes/re-enabling your configs one at a time until you find one causing the issue or until all errors are resolved.

If your issue continues, post your the Sitecore version you upgraded to, the version you upgraded from, and any modules you have installed as a comment on this post.