Sharepoint not starting - Error 503

At our office network we have a Sharepoint Server which also serves as the VPN Connectivity for the Office LAN. Since we use Sharepoint for centralized management of several documents and tasks it was a blow when the Sharepoint crashed.

An Error 503 message kept on coming whenever I browsed to the Sharepoint page from my PC. Seeking to troubleshoot it, first I restarted the Sharepoint Server taking care to do so by remoting in from our Exchange Server to which I had remoted in via its Public IP address. The Sharepoint server restarted but the issue persisted.

On suggestion from my boss I inspected the Sharepoint Services in Services.msc . There I found that a few of the Sharepoint related services had not started even though they were on Automatic. Some of them were manually started but the rest refused to restart. It was then that I became aware of the fact that the central account passwords for our domain had been changed just a few days ago. So as instructed by my boss I went to the Properties of each service and in the Log On section if the Logging in credentials was no local or network and in fact used a domain user account, I changed the passwords.

After changing the corresponding passwords for all the services, I once again restarted the services and all the Services started running properly. But the sharepoint was still down. At this moment I went to the Server Manager of the Windows Server 2008 R2 machine and saw that there were some errors in the Web Services, an error whose diagnostic said about an Application Pool related to the Sharepoint site not running.

So I went to Web Services > IIS > Application Pools and as mentioned some of the Sharepoint related Application Pools were not running. I started them manually hoping that would solve the issue but again it did not. It was then that I got a brain wave and as I went to the Advanced Settings section in Properties of these Application Pools I saw that some of them were using special log in credentials exactly like those used by the Sharepoint Services in Services.msc. So I changed those log in credentials for all Application Pools which had this special domain/user account listed with it and then I restarted those Application Pools.

Now the Sharepoint started working and issue solved