HELP! I CAN NOT ACTIVATE PRE-INSTALLED WINDOWS

KHANHLE205,

We will need more information from you in order to help resolve this issue. What computer model do you have? You mention you reinstalled Windows on the computer. Did you use an OEM version of Windows to install or a Retail version.  Depending on your computer Dell has ISO versions of Windows at the link below for downloading and installing. Not all computers are allowed to download. 

Windows Backup Media

You can Download a Windows 10 RS1 .iso and clean install with your Windows 7 OEM Product key:

http://dellwindowsreinstallationguide.com/download-windows-10-oem-and-retail-iso/ 

Thank you very much, I will try that later I can not download windows 7 with my pre-installed windows key.

My laptop model is XPS 15 L502X. My service tag can be seen on the uploaded picture which is 4VZNSQ1.

Hello, turns out windows iso file are not available for my service tag. So what is the windows key on the sticker at the bottom of my laptop?

I am confused. It should be a legit key, right? 

Again, here is a photograph of the sticker.

It is a legitimate OEM key yes - it can be used with a Dell OEM windows installation disc.  It CANNOT be used with any non-OEM locked installation media.

As I mentioned it can be used with a Windows 10 RS1 .iso.

It can also be used with a Windows 7 Retail .iso but phone activation is required so Dell branded Reinstallation Media is preferred for a Windows 7 reinstall.