Windows 7 - Install Used Windows 7 Professional Key on Another Computer

I have a question that I cannot find to be clear.

I used to have a Gateway P6831fx, and I installed Windows 7 Professional on it, a couple months later the motherboard died, so I am buying a new computer.

The new computer is a Toshiba Satellite L675D-S7052, it currently has Windows 7 Home Premium

When I spoke to a computer tech, he said that I would be able to use my existing Windows 7 Professional key from the Gateway on the Toshiba, to upgrade it from Home Premium to Windows 7 Professional, since simply putting my Gateway harddrive in the Toshiba wouldn't work, and when I upgrade using my Gateway Windows 7 Professional key I should wipe the drive.

Is this true? Can I do this? All information would be greatly healpful. If you need more information it can be provided.

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Update (If I was unclear):

I already have windows 7 professional on my gateway, I was wondering if I could use the product key from my gateway on my toshiba (to upgrade), since the motherboard died on my gateway.

The computer guy I spoke to said I can, but I read otherwise on other websites.

Toshiba = Home Premium (able to upgrade using key I was provided when I bought Windows 7 Professional?)

I don't have an installation disc, I bought Windows 7 Professional as a download (when I installed it on my Gateway), and was provided a key to activate Windows.

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From what I'm reading below it sounds like I can use the Key to Upgrade my new computer, am I correct? (Sorry I want to be absolutely sure.)

If it`s a retail edition ( store bought ) then yes you can. But why bother ? Do you absolutely need something that`s in the Pro version ?

^ I agree. I use both Win 7 Home Premium and Ultimate, and the differences aren't worth the major upgrade. HP does miss out on the Windows XP Mode though, although it wouldn't matter for most users.

If you can get hold of the Win 7 Pro disc you used for this installation, or a retail version from folks you know, nothing like it.

Providing your Windows 7 Professional DVD is the retail version you can use it to upgrade your Toshiba from Home Premium to Professional.

Windows Anytime Upgrade - Windows 7 - Microsoft Windows

You don't even need to insert the Win 7 Pro DVD, all you need is the product key, which you enter when asked.

You'll need to reactivate Windows on completion.

Activate Windows 7 by Phone

Type Anytime in Start Search box, insert the Professional Product Key, within minutes the extra features will be unlocked.

Be sure to store externally a Win Backup image before and after the Upgrade so you can revert to Home Premium if you want to migrate your retail Pro key elsewhere, or if you need to reinstall Pro without also reinstalling HP.

Backup Complete Computer - Create an Image Backup
System Image Recovery
Macrium - Image your system

Thank you everyone that has replyed, I will take all your advice, unfortunately I will be unable to try anything until next week, once I have done so I will reply again.

I would like to thank everyone for their help, you all made this process much easier.

You're very welcome Nicholas and thanks for the update.