windows boot file

[ms_b52]

Ok, I know I am going to be dubbed a ditzy blonde for this but here goes my dilemma I need some help with.
I accidentally went to the wrong pc at a friends house that needed to be set back to factory setting.  When he came in and told me I was at the wrong pc I had just clicked the set back to factory setting command and then i shut it off quick!  But...a file for windows boot up was deleted.  How can it be fixed without the windows program discs, since he has none.  Or,,,can it be done without the windows program disc?
Thank you...anyone..

[viking]

What windows (xp, 98, me, 2000) does he has? How did you shut it off? What error makes his computer? What displays about it? Where did you choosed for  factory settings? Why should that computer to be setted to factory settings?