HOW TO RESTORE WINDOWS 8 GUI BOOT-LOADER AFTER INSTALLING WINDOWS 7?

The actual presentation (graphical or text) depends on many properties that can be set to the entries in the BCD store. An easy way to restore the defaults for Windows 8, effectively restoring the graphical boot menu, would be the following:

1. Open an elevated command prompt inside Windows 8, for example via +X and then A.
2. There run the following command:
   bcdboot C:\Windows (C should be the letter for your Windows 8, change it if it's not)

That command will replace the boot files with the ones from Windows 8, set the Windows 8 menu entry as the default one and set the parameters in the BCD to the default ones hence next time you reboot you'll see the graphical menu.

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If for some reason you want to change and use Windows 7 boot menu you have at least 3 ways:

1. Changing the default entry to Windows 7:
   That you can do graphically with e.g. EasyBCD under the "Edit Boot Menu" section:
   
   Or manually in an administrative command prompt:
   1.1. Execute bcdedit /enum, you'll see something like this:
   
   1.2. Copy the identifier of your Windows 7 entry, in this case it'd be:
   {bd47b8fe-2713-11e2-a631-bc02f01697a2}
   1.3. Execute the following command (you'll receive confirmation afterwards):
   bcdedit /default {id}
   E.g.: bcdedit /default {bd47b8fe-2713-11e2-a631-bc02f01697a2}
2. Set displaybootmenu to yes in the boot manager entry (which as of now makes use of the textual menu without changing anything else):
   bcdedit /set {bootmgr} displaybootmenu yes (in an admin cmd, like before)
3. Delete or set bootmenupolicy to legacy in Windows 8 entry:
   bcdedit /deletevalue {id} bootmenupolicy ({id} is the one for Windows 8 this time)

After that when you reboot you'll see the classic boot menu, the later 2 ways allow you to have Windows 8 as the default entry.

http://superuser.com/questions/499675/how-to-restore-windows-8-gui-boot-loader-after-installing-windows-7 

1. Start from the Windows 8 installation medium.
2. Optionally, choose your keyboard settings.
3. Hit Shift+F10 to enter the command prompt.
4. Execute bootrec /fixmbr to update the main boot record just to be sure, partitions will remain.
5. Execute bootrec /fixboot to update the boot sector of the system partition.
6. Execute bootrec /scanos to add known OSes to the boot configuration data.