Why does this laptop shut down randomly and unexpectedly while running Windows 7?
More aboutsatellite l355 s7812 shuts windows
If this happens only with Windows 7, then it's most likely a software problem. What version of Windows 7 are you running (final release or release candidate)? Also, are you sure all your hardware drivers are updated?
Yes, with Windows 7, Home Premium. Updated all drivers that I could find.