Previously i was having windows 10 and Ubuntu 16 dual boot. After i found a glitch in Ubuntu i deleted the Ubuntu partition .After that when i rebooted i got the grub rescue error. I was unable to do something , Even the F8 keys did not work . So I made live CD of Windows 8 because windows 10 live USB was giving error too. and I installed the windows 8 and the as usual the windows 10 was stored in a windows.old folder . I have all my important software . I don't want to install again and install all the software again . So please help me If i can the recover the windows 10 from the windows.old partition .This may be of help to you : Follow Me -->
Also since the grub bootloader made itself default, once you delete the Ubuntu installation that would leave you with the grub rescue prompt as the boot files wasn't available anymore. If your system has a legacy bios then you could of loaded the windows setup then do a fixmbr and fixboot with cmd from the advanced menu or a startup repair for an UEFI setup.