Very simple. If it doesn't have a recovery partition installed, you have to get the restore disc (Ebay or PC manufacturer) OR the correct disc for your OEM COA sticker on the computer. This is NOT a hardware question, so better to post in the operating system that you are licensed for for more specifics. Also, you should have posted more information - brand, model (that model did not compute when I searched), operating system, etc.
You can download Vista and Windows 7 from legal sources if you just search for it.
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