Installing and activating Windows 10

Windows 10 still runs and still activates normally, even though free support from Microsoft ended in October 2025. If your computer does not meet the Windows 11 requirements, this is the sensible choice — what the end of support means in practice is covered in a separate article.

If Windows 10 is already installed

  1. Open Settings → Update & Security → Activation.
  2. Choose Change product key.
  3. Enter the 25-character code from the e-mail and click Activate.

Final check: press Windows + R, type slmgr /xpr and press Enter. It should say the machine is permanently activated. More checks are in the article on checking your licence.

If you are installing Windows 10 from scratch

Before you start

  • A USB stick of at least 8 GB. Its contents are erased — move your files off it first.
  • A backup of anything important if you are doing a clean install.
  • Windows 10 has no TPM 2.0 requirement, so it runs on older machines too.

Step 1 — download Microsoft's tool

Open the official Microsoft page for Windows 10 and choose Download tool now. This downloads the Media Creation Tool.

Do not download Windows from anywhere else. The installer is free and comes from Microsoft — you only pay for the licence.

Step 2 — make a bootable USB stick

  1. Run Media Creation Tool and accept the terms.
  2. Choose Create installation media (USB flash drive, DVD, or ISO file).
  3. Leave the language and edition at their defaults unless you need something else.
  4. Choose USB flash drive and select the stick.
  5. Wait for the download to finish.

If Media Creation Tool will not run, download the ISO from the same page and build the stick with Rufus.

Step 3 — boot from the USB stick

  1. Leave the stick plugged in and restart the computer.
  2. Immediately after it starts, tap the boot-menu key — usually F12, F9, Esc or F2, depending on the make.
  3. Pick the USB stick from the list.

If the computer still loads the old Windows, go into BIOS/UEFI and put the USB stick first in the boot order.

Step 4 — install and activate

Follow the steps on screen. The key can be entered during the install or afterwards — the result is the same. For a clean install choose Custom and select the partition.

Once the system is up, activate it using the steps from the first part of this page.

If something goes wrong

  • The key is rejected — usually the edition does not match: a Pro key will not activate Home, and the other way round. The remaining causes are in the article on activation errors.
  • Windows deactivates after a hardware change — activation is tied to the motherboard. The fix is in the guide to transferring a licence.
  • Nothing helps — write to us at info@litsenzi.bg with your order number and a screenshot. We help free of charge, and if the key really does not work — replacement or refund.

Don't have a licence yet?

Windows 10 Pro adds BitLocker, Remote Desktop and domain join over Windows 10 Home. If your computer meets the requirements, it is worth looking at the comparison with Windows 11 as well, because support there runs for years yet.

The key arrives by e-mail, usually within 15 minutes during business hours, together with an invoice.