I received this "Service Unavailable" error when trying to connect Team Foundation Server 2010.
As a TFS administrator, my first thought is that the system is offline. So I logged on to the TFS server and found that the system is still running, but when I go to IIS and try to run the Web, it doesn't work either.
After much digging, I found out that the application pool for TFS stopped working because I changed the password for the TFSSERVICE account through Server Manager, but didn't change it in the application pool.
Here's how to fix it:
Please note, I'm using IIS7.
1. Open IIS (type InetMgr).
2. Left click on the tfs site that stopped working (for me, the tfs site is called TFS1Server)
3. Select the "Adavnced Settings..." on the "Actions" panel. From this Advanced Settings panel, you can see which Application Pool your TFS website is using. For me, I used the default application pool called "Microsoft Team Foundation Server Application Pool"
4. Now select "Application Pools" in the "Connections" panel. You will see the "Microsoft Team Foundation Server Application Pool" showing up in the Application Pools panel.
5. Select "Microsoft Team Foundation Server Application Pool" and select "Advanced Settings..."
6. In the "Advanced Settings" popup window, locate the "Identity" line, then click on the "..."button.
7. When it pops up, choose Custom Account, select "Set..."
8. In the "Set Credentials" popup screen, set user name and password, such as "TFS1\TFSSERVICE", etc.
9. If you also configured the Web Access Application Pool, then you should set the password for this pool as well.
Restart IIS, you are done.