When you install UAG, it adds a long list of services to the system, as well as a lot of dependencies between themselves and other system services. For example, without the TMG services running, UAG won't even let you open the configuration console, and the TMG services themselves depend on the Secure Socket Tunneling Protocol Service. A clear sign of something going wrong is an onscreen message that says some services could not be started, but if the server starts to behave strangely, begin by inspecting if all services that are set to "automatic" are indeed started. This can be seen in the Services administrative tools, which allows you to sort the list of services by startup-type.
Here is a list of services that are required to run for UAG to function properly, including services that depend on them:
ISASTGCTRL
Base filtering engine
COM+ Event System
Microsoft Forefront TMG Control
Microsoft Forefront TMG Firewall
Microsoft Forefront TMG Job Scheduler
Microsoft Forefront TMG Managed...
