How to Install Windows 11 on a Dell Optiplex 990 (and perhaps other older hardware)

To perform a clean install

1. Configure the BIOS
   • Set boot mode to UEFI
   • Set SATA configuration to AHCI
   • Enable Secure Boot/TPM
2. Prepare a USB drive
   • Use Ventoy to create a USB drive
   • Copy the win11 ISO to the data partition of the drive
3. Wipe the drive during the install process
   • Boot from the USB
   • When you see the “Where do you want to install Windows?” screen press Shift + F10 to open a command prompt
   • Then type the following commands, in this order
     • diskpart
     • list disk and choose the drive onto which you want to install. Most likely Disk 0
     • clean, this will remove all data from the drive
     • convert gpt, this is the command that will make the drive UEFI-compatible
     • exit
     • exit
4. Continue with the installation. When it asks you where to install, select the drive you just wiped. It should list a large “Unallocated Space”.
5. Select it and click Next
6. It will then show a blue screen with “n% installing”
7. Keep an eye on it and when it reboots, remove the installation USB
8. You should see a “Getting Ready”, or “Installing 0%, Please keep your computer on” message. If you get there you on your way to installing Win 11 on your computer.