Download and burn the Windows 10 .iso file, boot from it, and use the option to go back to Windows 7 or 8 or 8.1 (you didn't tell where you came from, so I mention all possibilities).
Kees
I had an alert and downloaded Windows 10. When it loaded there no Start menu.
A lot of forums suggested opening powershell in admin and inserting Get-AppXPackage -AllUsers | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}.
That didn't work so I tried another tip from the MS forum whereby you go into the Registry Editor and insert:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\ ImmersiveShell\Launcher Click Edit > New > DWORD (32-bit) Value, and name it UseExperience. Double-click the newly created item and set the value to 0.
Since then my laptop refuses to start-up at all, it says it is diagnosing the problem and then goes to automatic repair. Reset the PC doesn't work, system restore doesn't work, system image recovery doesn't work, check disk in the command prompt bit doesn't work.
I also tried...
bootrec /fixMBR
bootrec /Fixboot
bootrec /rebuildBCD
I'm at my wit's end - is my laptop dead?? Any tips/suggestions?? everything was fine before I tried to install the new windows, now I have a completely non-functioning laptop.
Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic