Re-installation of Win XP Media Edition

> Hello,
>
> I accidently deleted some system file from my desktop PC and since then I
> have not been able boot up my PC. I get error messages indicating that some
> of hard drives are not present any more. I then re-booted using the
> installation disk provided by Dell. This still gave me the same error
> messages but I was able to run windows. however I now have the operating
> system in two directories at the moment.
> Also, now the PC does not seem to pick up any of the audio video cards
> although they are all there and in working order. Also, I can no longer see
> the Program Files (office, etc) although I can see that they are all there
> when I search for them via Explorer.
>
> Could someone advise me on how sort 1) operating system and 2)being able to
> see my programs.
>
> thanks
>
> M