Windows shut down automatically

I had just re-installed the Windows XP Professional to my Fujitsu Table PC. However the system shut down automatically every half to one hour. Before shutting down there is error messages reads as follow:

The system is shutting down. Please save all work in progress and log off. Any unsaved changes will be lost. This shutdown has initiated by NT AUTHORITY\SYSTEM
Message:
The system process ??C:\WINDOWS\system32\lsass.exe?? terminated unexpectedly with status code
-1073741819. The system will now shut down and restart.

Please help to solve the problem
Thank you and regards
natterjack