Hi Wei Peng,
Here are a couple of things I would check.
#1 - Launch the Altiris Log Viewer (All Programs > Symantec > Diagnostics). Use this tool to verify that no errors are occuring when you bring up the IA navigation and when you click the Home tab.
I have see a problem when the ProductVersionItem has not properly been defined in the PAC which caused navigation icons to be broken. These errors were raised in the log viewer.
#2 - Have you tried another browser? I know there are etrack issues logged with IE which are resolved by using Firefox as a workaround. See etrack 2221090.
#3 - have you debugged through your SSO code to see that it is properly executing through your code flow and redirecting to the appropriate page?
You may want to query your group's assigned support engineer to dig deeper into the problem if the above does not resolve your issue.