I had Vista on my system. I installed Win 7. But forgot to note down the key for Vista. The sticker on the back of the laptop has faded too & nothing is readable.
Is there any way I can get Vista key?
“If I use a Windows 7 Upgrade disc to upgrade my Windows Vista Laptop to Windows 7 or clean install Windows 7 , can I then use my Windows Vista disc and product key to install Windows Vista on another Laptop?”
No. The Windows 7 Upgrade license replaces the previous Windows Vista (Windows XP) license.
To be clear: your old version of Windows that you upgraded from can no longer be used on your current, or any other, computer.
Is the above answer correct? I found this in a forum.
Yes it is correct 
You only paid for a upgrade to Win 7 not a full version. (ie:- you paid a reduced amount for upgrade)
Can I reinstall Vista back on the system?
Yes you can on the same computer.
It is possible the Vista key may still be in the registry if it was a upgrade to Win 7
Sorry I cannot help you with the key you need to search for a program that can find keys in the registry.
Maybe someone will post a suggest program.
Try this
I did clean install & not upgrade.
I tried SIW software & it found Win 7 key as Win 7 is installed, no Vista key.
I thought I will reinstall Vista back on this system. And will use Win 7 Upgrade disc to install Win 7 on new system, I googled & found that many people installed Win 7 on new system with Win 7 Upgrade disc.