“Service Unavailable”

When you browse a Web site, you may receive the following error message:

“Service Unavailable”

CAUSE
This issue may occur if the application pool for the server is configured incorrectly in Internet Information Services (IIS). This issue may occur due to the following reason:

• The application pool is not running.

RESOLUTION
To resolve this problem, you have to follow the following tweaks:

Verify that the application pool is configured for the server. The default application pool is MSSharePointPortalAppPool.

Follow these steps to determine the application pool that the virtual server is using:

(a) Click Start, point to Administrative Tools, and then click Internet Information Services (IIS) Manager.
(b) Expand ServerName, expand Web Sites, right-click the virtual server, and then click Properties.
(c) Click the Home Directory tab.

The application pool that is configured for the server is listed in the Application pool box. Try to switch it from MSSharePointPortalAppPool to DefaultAppPool Or vise-versa; if the domain has it own application pool switch the same to that particular application pool.

(d) Click OK.

NOTE:
If the domain is already assigned with an application pool. Then you have to recycle the particular application pool.

Take some efforts to Search the forum little bit and u will fine the post for “ Recycling the Application Pool “