My computer is a mess need help

I have a Dell inspiron and was having troulbe with it going slow,So my grandson reinstalled windiws vista but he put it on recovery d and maxed it out,i deleted all that now when i start my computer it goes to Windows boot manger where I have to choose between Microsoft windows vista OR windows vista I do not have disc or i would just reload it,I've been tring to get to Dell factory image restore,or any other place that will let me restore it to out of box state any help out there

thanks  if you can help Bill