windows cannot connect domain either domain controller is down or otherwise unavailable or because your computer was not found

The resolution and workaround to solve the error is as below.

1. Login to the Windows 2003 domain controller, and delete the computer account object from the Active Directory by using Microsoft Management Console (MMC) which you can always access from “Manage Your Server”.
2. Log-in to the PC workstation as local administrator. If you cannot logon as local administrator, try to unplug the network cable and logon to the computer by using a domain administrator user that used to logon on the PC before, by using cached logon credentials feature.
3. Go to Control Panel, then click on System icon, then go to Computer Name tab.
4. Unjoin the computer from the domain by clicking on “Change”. You should see that Domain button is now selected. Remember your domain name in the text box. Select (Click) on “Workgroup” to remove the computer from the domain, and put any workgroup name in the text box (e.g. workgroup).
5. Click OK to exit.
6. Restart the computer (optional)
7. Go back to the Control Panel, launch System properties and then go to Computer Name tab, and click on “Change”.
8. Rejoin the domain by uncheck the Workgroup button and select (check) Domain button, and put in the domain name noted above into the text box.
9. Click OK to exit.
10. Reboot the PC.

try to ping DC Computer ip, if it ping then restart your Computer and try Again
if it does not ping then check with Internal Settings

Sanjay Limbu's solution worked for me. In active directory, under computers... the computer name was disabled and had a big red X on it. Right click and enable this computer... bam, the user could log back in. You do not have to remove the PC from the domain or the user from the active directory list.