Out of the box, Office Web Apps has issues if it is installed on a domain controller. To get around of this issue, this script needs to be run.

Please do note that Office Web Apps is not supported on a DC. This configuration should only be used for demo/development purpose. It should never be used in production.

For details of the issue see FAQ: SharePoint 2010 RTM Installation.

PowerShell
Edit|Remove
#Enable Word Web App: 
$e = Get-SPServiceApplication | where {$_.TypeName.Equals("Word Viewing Service Application")} 
$e.WordServerIsSandboxed = $false 

#Enable PowerPoint Web App, you need to answer "Y" after each command:
Get-SPPowerPointServiceApplication | Set-SPPowerPointServiceApplication -EnableSandboxedViewing $false
Get-SPPowerPointServiceApplication | Set-SPPowerPointServiceApplication -EnableSandboxedEditing $false

#Don't forget to do a iisreset after those commands!