Hi Mehra,
Check with the location "drive"\program files\altiris\altiris agent\ you can find SMA files. check with the windows event log for more information why it stopped.
How did you install the agent? push, pull or manual installation.
What is the version of SMP?
If the SMP version is 6.0, we can try with the article provided above.
Provide us more details so that we can provide solution.
Regards,
Siva