Solving SharePoint Server 2010 - 503. The service is unavailable, After installation

Question

I got a 503 error because the Application Pools weren't started in IIS for some reason.

1) Ensure that the enable32BitAppOnWin64 setting for the "SharePoint Central Administration" app pool is set to False, and the same for the "SharePoint Web Services Root" app pool

2) Edit applicationHost.config:

bitness64 being the magic word here

I agree with Beytan Kurt.

I had 503 thrown for both the Central Admin site as well as the SharePoint landing page. In both cases the Passwords were expired.

After resetting the password in the AD, and refreshing the Identity, CA worked but the SharePoint landing page threw a 500 error.

It turned out that the .Net Framework Version was set to V4.0. I changed it to V2.0 and it worked.

Remember after each change you need to recycle the appropriate app pool.

Can You Please try this : Check the web site properties in IIS. Under home directory tab, check the application pool value Verify that all SharePoint services are started. If the application is not started do the following: I think this error might occur because of changing the service account password. You may need to change the new password to application pool
1)Click the stopped application pool 2)click advanced settings 3)Identity ->click the user to retype the user 4) Application Pool Identity dialog 5)click set -> manually type the user name and password. Then restart the server.

It can also happen if your password policy or something else have changed your password in case your appPools are using the the user with changed password.

So, you should update the user password from the advanced settings of your appPool throught "Identity" property.

The reference is here

I had trouble finding the applicationhost.config file. It was in c:\windows\System32\inetsrv\ (Server2008) or the c:\windows\System32\inetsrv\config\ (Server2008r2).

After I changed that setting, I also had to change the way IIS loads the aspnet_filter.dll. Open the IIS Manager, go under "Sites", "SharePoint - 80", in the "IIS" grouping, under the "ISAPI Filters", make sure that all of the "Executable" paths point to ...Microsoft.NET\Framework64\v#.#.####\aspnet_filter.dll. Some of mine were pointed to the \Framework\ (not 64).

You also need to restart the WWW service to reload the new settings.

The selected answer posted here solved one problem, but another is that you'll have to change the app pool to use .Net 2.0.

"SharePoint 2010 uses .NET Framework 3.5, not 4.0. The SharePoint 2010 app pools should be configured as .NET Framework 2.0 using the Integrated Pipeline Mode."

source: http://social.msdn.microsoft.com/Forums/en-US/sharepoint2010general/thread/4727f9b4-cc58-4d86-903b-fabed13da0ff