Melikia.....no i havent diagnosed it yet. It started like 4 months ago. First I thought it was something not important, then it happened usually  over weekend looking like my Toshiba taking days off.....My friend  said it could be some kind of virus....i cleaned everything, dig into registry and stuff, and it seemed to help, but not for long. Now I believe it's overheating issue....dont want to spend money for @repairing@ it, but at the same time quite afraid of opening it myself and clean  the fan...as they did for my  friend with another Toshi....The plan was to sell it and buy some nice quad core, now I can' do it knowing it;s not working properly....:(