Help with restting mylptop to factory setting

Hello,
hi there i have a toshiba sat l300 its come up with a blue screen and to put a password in i dont no what it is also i think i got a virus or something on there cause before the blue screen with password came up it never done anything was just a black screen with a white flashing line in top left hand corner. how do i rest this back to factory settings or get this working again without a disk x