My PC has Win10/Win7 installed with dual boot. I will be presented with a selection menu where I can select whether to boot Win10 or Win7.

I have my Win7 installed on Disk 0 (C Drive) and Win10 on Disk 2 (J Drive). But I lost my Win10 password (That's stupid - I know) and I couldn't login back to Win10.

There is nothing serious yet on the Win10 system. So I thought I can just reboot the PC and reinstall Win10 with the DVD.

Things get complicated when I read the options from the installation disk which I am not so sure if the installation will touch my Win7 installation (It shouldn't because that's how I install Win10 in the first place - anyway, doesn't matter anymore). So, instead of proceeding with the normal repair/reinstall option provided by Win10. I have reformatted Disk 2 (Drive J) and restart the computer.

I was expecting the Win10 start up disk will take this as another fresh installation. However, it is smart enough to know it was not. I got a start up error message but I can proceed to boot with Win7 so it is not the end of the world yet.

Any thoughts on how to re-install the Win10?

Disk Configuration


I am able to reinstall a new Win10 just to give up the original boot menu. The newly installed Win10 got its own boot menu. I can still able to access my Win 7 by changing the boot sequence in BIOS every time if I want to. It is annoying but not the end of the world though.

enter image description here

I suppose I can work something out using bootcfg command later

  • Are you actually trying to get rid of the boot entry of Windows 10 on the boot menu? It's not clear at all what's the problem/obstacle you bumped into. – Tom Yan May 8 at 5:43
  • You said you don't know if it will touch your Win 7 and then give up on reinstalling but then you installed it just like that before but then you get start up error message but then you don't know how to install Win 10 now? That's not really making sense. – Tom Yan May 8 at 5:45
  • "I got a start up error message" Maybe I missed it but what was the error message? – Discant May 8 at 5:55
  • @TomYan Thanks for your comment! Yes you are right. It was just a flash in my mind. I had no problem install for the first time because I know Win 10 will create a boot menu to allow me to boot from either OS. But for the second time, I wasn't so sure back then. – chapter3 May 10 at 1:08
  • @Discant Thanks for the help! The screen show up right during the initial boot so not able to get a screen capture. It should be saying something like "boot device missing". Apologies couldn't get the exact error message now. – chapter3 May 10 at 1:11

If both drives are mounted, take into account the size of each partition in megabytes (MB) and/or gigabytes (GB). You can easily piece from there which partition is the Windows one, regardless of whether or not they are showing up as disk 2: partition 0 in the boot disc.

  • Look, it's not wrong. You can piece together which partition is which by taking into account the file size. – WG481 May 8 at 18:23

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