Safe Mode sudden shut down

Toshiba laptop running Vista Home.. 2 GB ram..just did a factory recovery and my problem is...normal mode runs fine...however, whenever I am in safe mode and run mbam or sas or my defrag or most any other programs, the laptop will suddenly shut down...this happens in safe mode only..in normal mode, everything seems to run fine and this has been happening hence the factory recovery...I can not find an answer anywhere as this seems to be a "backwards" problem, usually it's normal mode that suddenly shuts down, mine just shuts down in safe mode..a scan with nortons 2010 and mabam and dr web show nothing and even a hijackthis scan reveals nothing abnormal as this is a new install...what could possibly be happening?