Don't you actually need to buy a new license? I don't think you can activate any 3rd party installer (say downloads via microsoft.com, making an usb key) with the oem serial? Not sure though, the only windows license I'm currently using isn't OEM, it's a full 8.1 pro license.

This does sound like a good argument for wiping the OEM windows 7 pro partition on my laptop, and install a windows 10 trial or something (I currently just run Debian GNU/Linux on it -- but it's technically dual-boot).

Dell is about the only manufacturer that will let you get generic install DVDs. They use a bios based licensing system these days so you don't even have to deal with those issues so much.

http://en.wikipedia.org/wiki/System_Locked_Pre-installation

Don't know why you are downvoted. Before I switched to Mac (now I know what a good choice I made!), I find that installing fresh Windows without piracy is incredibly hard. The so called OEM embedded serial key works only sometime; Other times, the fresh Windows will ask me to buy and activate it. Utterly confusing even for a techie like me.

So I installed a pirated Windows.

Dealing with the windows tax crap is hardly news, buying new overpriced hardware to benefit from a golden prison is neither an acceptable solution for somewhat facing the issue nor what a techie would do.

The easy option is to phone microsoft support and explain the problem, you most probably will be given a new valid key. Other options for techies includes using OEM install medium or installing a free software OS.

Nowadays there's no licence key to type anymore, it's included in the hardware sold with windows 8 (which is worse).