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Dual boot and uefi problems.


New Member
I have a new laptop, a toshiba p870, that came with windows 8 preloaded. I needed windows 7 for compatibility reasons with a few programs and after a bit of research and struggle I eventually got it installed on a second hard drive in the computer but in the process I had to change the bios settings to disable secure boot and enable CSM. After that Windows 8 will no longer boot even if the second hard drive with windows 7 is removed. I have no way to access the bios in order to change this setting back, the only way to access it was by going through the windows 8 recovery and troubleshooting settings, inserting a windows 8 disc (from a previous installation on a different computer, non-uefi) didn't offer the uefi firmware options in recovery mode. What can I do to restore access to windows 8 on this system?

EDIT: I finally figured it out. You must hold shift as the computer shuts down in order to get the toshiba logo and the option to enter the bios with F2 to show up at startup. This isn't a very convenient setup for dual boot, having to change between CSM and UEFI to choose operating systems but it works.
Last edited:

My Computer

System One

  • OS
    windows 7 & 8 pro


New Member
Pro User
Could you get us a picture of the Disk Management window to include the graphical partition info. Maybe it will help us see what is going on. You can use the snipping tool to take the picture and then attach on the Advanced replies.

But glad you got it to work...

My Computer

System One

  • OS
    Windows 8.1 x64
    Computer type
    System Manufacturer/Model Number
    Home Grown
    i7 3770K
    ASUS P8Z77 -v Pro, Z87-Expert
    16 G
    Graphics Card(s)
    EVGA GTX 680 Classified (2)
    Hard Drives
    Kingston SSD 240 GB


VIP Member
VIP Member
Gold Member

You to do step 3 first.

theog said:
3) Reset BIOS to default, and reboot to BIOS make sure Secure Boot is disabled.
Make sure CSM is ENABLED, & set to UEFI boot.
NOTE: Check your manufacturer's uEFI BIOS manual for settings.

How to enable CSM for a Toshiba.(Satellite Pro C870, Satellite Pro L830, Satellite Pro C850, Satellite Pro R950, Portege R930, Portege Z930)

Toshiba said:
To downgrade from a installed Windows 8 OS to a Windows 7 OS, using a Windows 7 recovery media, follow these steps:

1) Boot unit and press F2 to get into BIOS

2) Go to "Security" tab and disable "Safe Boot"

3) Go to "Advanced" tab, select "System Configuration" then change boot mode from "UEFI" to "CSM"

4) Press F10 to save changes and exit.

5) Boot unit from recovery media (Press F12 on bootup to boot from USB or DVD media)

6) At the first screen prompt during recovery, double click on the top left hand corner to open a command prompt

Steps to Install Windows 7 on a Windows 8 Unit
Necessary changes in the UEFI Firmware (BIOS) for a successful downgrade from Windows 8 to Windows 7

Toshiba How-To: Resetting your UEFI Bios Firmware on Windows 8 - YouTube
How To: Enter the system BIOS or UEFI in Windows 8 - Toshiba Forums

My Computer

System One

  • OS
    ME, XP,Vista,Win7,Win8,Win8.1
    Computer type
    Other Info
    Notebooks x 3

    Desktops x 5

    Towers x 4