my advent 7106 keeps switching off

Hi iam having a problem with my laptop which is a advent 7106.It keeps switching off on its own and it mainly happens when iam using dvd shrink or converting it dosent even shut doewn it just gose off.I have had it for abought a year and a half and it happend about six months ago and i manged to find help after typing in to goggle but now when i do it i cant find anything to help.I hope some one can help.thanks in advance.torres9