How to get back my old os activation code?

i got a trial version of windows 7, but i was such a idiot that i forget to backup my computer, i have vista before i change my os. the papers that came with my computer was lost a year ago. my 30 days trial is almost over. please help me.How to get back my old os activation code?
if windows 7 demo got a option on upgrading with a serial look up windows 7 serials on google and put them in and that will fix it :P if not say goodbye cuz once 30 days iz up u cant log in so hurry son lolHow to get back my old os activation code?
you could try running a free app called belarc, but it may be totally gone if you upgraded your OS

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