I have a windows 8 pre installed pc. I tried to dual boot Ubuntu with it by allocating a separate partition. The installation of Ubuntu went well but it didn't boot up.

Windows 8 only booted us as soon as i started the pc. So  i went around and changed the settings of UEFI/LEGACY modes, secure boot,etc and nothing worked!  Finally i installed ECBCD and added an entry for Ubuntu manually. After restarting boot menus shows two Ubuntu operating systems and neither of them are working. It shows ERROR LOADING OPERATING SYSTEM!

I tried using my recovery cd to repair/reinstall my windows 8 os but it also says cannot find windows 8 aka the NO SUITABLE OPERATING SYSTEM IS FOUND. Is there any way that i can use tools like BCDEDIT to change to windows  8 boot menu (without affecting windows installation partition)?

I shall suggest you to kindly follow the necessary steps as described in the following article first:

Guide To Install Ubuntu 14.04 In Dual Boot Mode With Windows 8 Or 8.1 UEFI

Hi Vasanth,

What steps you have tried to fix the Windows 8 bcd?

We can try the following steps to have a repair.

1.We can try to boot from the installation media. Choose the repair mode then choose "Startup Repair" to have a repair.

2.We also can try to open a command line and use the command line to have a fix. For the message "NO SUITABLE OPERATING SYSTEM IS FOUND", we can try to use the command line "bootrec.exe /ScanOS" to have a check.

3.If issue persists, we can try the following command line:
bootsect /nt60 c: /force /mbr      ( command, /nt60 = use boot code that is compatible with BOOTMGR, / = force dismount, / = write mbr )
 ( bootsect does to touch mbr, it works on the selected drivesahem.wait for itbootsector)
bcdboot c:\windows /s c:   ( command, look in c:windows for files, copy files to c: (actually c:\windows\boot) )

Best regards