Windows XP Repair(something to do with HDD) PLEASE HELP!

hey, my friend asked me to fix his laptop. here is the story. he phones me up asking for help as his laptop turns on and reaches a screen saying some file(ending with system, dont know exact details sorry) is missing and it can be repaired by inserting the windows disk. thats all fine. so i insert the disk and i press R, then it says something about HDD cannot be detected or it is not turned on. just to clarify there is one present..
so then we try the full installation, again with the error. please can you help me out. i do not have the laptop with me right and do not know any numbers of the laptop but if i can get a picture of what to do, that would be great. thats v much for any help. thanks!