Usually, if its 1 machine then I suspect it alone. If all the other machines are working ok, then its highly unlikely its LANDesk or even your image/configuration. I'd go through the event logs and look to see if there is a problem with the system. Try upgrading the BIOS and ensure all the latest drivers are installed. Maybe rebuild it again and see if the same thing happens. If it does, then it it problem something hardware related.
Are all the T500's are getting the same agent? If so then the next most likely problem I can think of would be the video card. Is the video card (or drivers) different in any way on this particular T500? When the agent installs a Remote Control Mirror driver usually installs as a default. In a few rare cases that I've seen the mirror driver fails to install correctly but the agent appears to finish installing anyway. A test for this might be to completely remove and reinstall the agent without the mirror driver. If remote control starts working then the device may have mirror driver issues.I would also check Device Manager. Once or twice I've seen multiple mirror drivers installed which can also cause a problem. Running uninstallwinclient.exe may (or may not) take out one of the drivers.
Also, Agent Discovery in LANDesk 9.0 is being reworked (http://community.landesk.com/support/docs/DOC-10347) and may not provide correct icons. You can manually test Agent Discovery on a particular device using a browser:
The first link should produce a LANDesk banner. The second link should just produce garbage. If you don't receive garbage on the second link then either traffic is being blocked (firewall) or the Remote Control Service wasn't installed correctly.
If needed you can also launch remote control manually but the service on the client will need to be functional.
Thanks to those that replied, mentioning the drivers helped to get me searching in the right direction.
I was getting the “TrueVector driver: Driver install or load failure: LoadNTDeviceDriver error message repeatedly in the Application log and discovered that it had started to occur the day that I installed theCisco VPN client v4.8.01
Uninstalled/reinstalled the VPN client and the turned off the ‘stateful firewall’, problems gone. Can now see remote control icon against device in console, and can remote in just fine. The "Type" column in console still shows "Workstation" instead of "XP Workstation" but I can live with that.