Downgrading from Win 8 to Win 7 - Error:0x80300024

I need assistance as I can't figure out what I'm doing wrong. I have a dell XPS 15 L521x laptop that I am downgrading from Win 8 to Win 7. I'm installing from a DVD. I'm attempting to install Win 7 on a 120GB SSD. Windows 8 was installed on a 2.5 inch 1 tb drive.

I have followed the following instructions in red. I hit a problem at "Where do you want to install Windows". I choose my partition and click next. I get an error message at this point "Windows is unable to install to the selected location. Error:0x80300024." The Disk does show up as Disk 0 Partition1:Windows 7 and has been partitioned to 120GB. Not sure how to proceed.

Boot into BIOS setup, if this is a new Win8 PC look for a setting to disable Secure Boot. Then enable Legacy BIOS or Compatibility Support Module (CSM). This should remove any EFI Boot Disk from BIOS Boot order. Set DVD drive first to boot, HDD second. Then set SATA controller to AHCI. Save changes and Exit.

Then boot into installer DVD or flash stick burned or written using tool and latest ISO for your licensed OS version here.

At first installer screen Press Shift + F10 to open a Command Box, type:

DISKPART
LIST DISK
SEL DIS 0 (after confirming Windows 7 target HD #)
CLEAN
CONVERT MBR
CREATE PARTITION PRIMARY SIZE=102400 (for 100gb partition, adjust as desired)
FORMAT FS=NTFS LABEL="WINDOWS 7"
ACTIVE
EXIT
EXIT

Thank you for your response. Yep, I went through all the steps below and no problem in following any of the steps. Only when I get to the clean install part. I also changed the bios settings. The only thing I did not do is unplug the other hard drive as this is a laptop. I didnt open up the laptop to unplug the 2.5 drive. I will see if I can do this but I doubt that I can.

At first installer screen Press Shift + F10 to open a Command Box, type:

DISKPART
LIST DISK
SEL DIS 0 (after confirming Windows 7 target HD #)
CLEAN
CONVERT MBR
CREATE PARTITION PRIMARY SIZE=102400 (for 100gb partition, adjust as desired)
FORMAT FS=NTFS LABEL="WINDOWS 7"
ACTIVE
EXIT
EXIT

theog said:

To Downgrade to Windows 7.

Downgrade Windows 8 to Windows 7

Warning you must have the uEFI/BIOS firmware setting in Step Three set.

theog said:

3) Reset BIOS to default, and reboot to BIOS make sure Secure Boot is disabled.

NOTE: Check your manufacturer's uEFI/BIOS firmware manual for settings.

Make sure CSM is ENABLED, & set to UEFI boot.

   Note

You may also need to

enable Boot Menu.

enable BIOS password.

Technical Note: UEFI BIOS vs. Legacy BIOS - YouTube

theog said:

3) Reset BIOS to default, and reboot to BIOS make sure Secure Boot is disabled.
NOTE: Check your manufacturer's uEFI BIOS manual for settings.

How to enable CSM & disable Secure Boot for a Dell.

Dell said:

To access the System BIOS on your Dell computer, you must enable an advanced startup mode. To do this, follow these steps:


Swipe in from the right side of the screen, or hover your mouse pointer in the top right corner of the screen and drag down to bring up the Charms menu.

Select Settings, then select Change PC Settings.

Select the General tab.

Under the Advanced Startup section, select Restart Now.

When the computer restarts, it will enter an advanced options menu. Proceed with these steps to enter your System BIOS:

Select Troubleshoot.

Select UEFI Firmware Settings.

Select Restart.
The computer will restart again, and this time it will enter the System BIOS. Locate the setting for Secure Boot, and change it from Enabled to Disabled. Save your changes and exit the System BIOS.

How to Downgrade from Windows 8 Pro to Windows 7 Professional

Sign In to Your Dell My Account

Sign In to Your Dell My Account

The problem may be that while you disabled Secure BOot, you still have UEFI enabled and need to follow the steps Theog gave above to enable CSM for Dell.

Otherwise you can install in UEFI (Unified Extensible Firmware Interface) - Install Windows 7 with - Windows 7 Forums.

To understand more about the difference between UEFI and BIOS watch this video: Technical Note: UEFI BIOS vs. Legacy BIOS - YouTube