Oh dear. If you want to get it back,then you will need the disc! Unfortunately, if it was preloaded on your computer, you may not have this available. If you cannot borrow one elsewhere (and you will need your own serial number as well,) then your best bet is to download a copy of Open Office which is a free Microsoft office replacement, opening most word, excel and so on files. To get it merely google it to get the web address for the download.
P.P.