When i play rome total war the game is fine until about 15 minutes in and it randomly shuts down my whole comp?

when i play rome total war the game is fine until i do the campaign and then it freezes and shuts down with no warning , no error messages . but say i play online battles it works perfectly .It use to work fine and has only started doing this recently . I have tried reinstalling it but the same thing happens and it is not a pirate copy of the game i bought it off steam for �5 . i have tried contacting steam support but they are useless and take ten billion hours to reply . my graphics card is:Nvidia Geforce 9300m GS . which as far as i know is sufficient enough to run this game also im on windows vista with an acer laptop .PLEASSSSSSSSSSEEEE HELLLLPPPPPPP!!!!!!!!!1