How to fix Grub rescue problem

Question- I just deleted a partition I was having alongside Ubuntu. But when I restarted my Windows 10 it showed me the error "no such partition. Entering rescue mode...". Then I tried using a DVD with windows10 with it but I had an error "recovery...signature of file couldn't be verified.

Method - 1
You should have fixed the bootloader first, but a setup disk can do that.
Fix the bootloader of all versions of Windows since Vista (for XP you can use a Vista or newer CD that boots and instead of /nt60 write /nt52, though the newer boot sector should be able to find ntldr too)
You'll need to launch any recovery/installation disk with Windows Vista or newer, use its recovery options to open a command prompt, and in that one the command bootsect /nt60 ALL /force /mbr will fix all the partitions' boot code (Windows 7 activators get affected by this)
The "rescue mode" message depicts that even after deleting the Ubuntu partition, the grub bootloader has not been removed.

I think your Windows 10 copy is not a genuine copy (as trusted by the windows and hence there is a signature/certification error) and so it won't invoke the recovery option. All you have to perform the following steps with a Windows 7/8/8.1 installation/Upgrade disc.

Method-2
Put the Windows disc in the disc drive, and then start the computer (set to boot from CD in BIOS).
Press a key when you are prompted.
Select a language, a time, a currency, a keyboard or an input method, and then click Next.
Click Repair your computer.
Click the operating system that you want to repair (Windows 7 in this case), and then click Next.
In the System Recovery Options dialog box, click Command Prompt.
Once in the command prompt, type exactly Bootrec.exe /FixMbr and then press ENTER. You will see "operation completed successfully." (Doesn't even take a second. Don't be alarmed )
Reboot and set BIOS to boot from the HDD again.
GRUB will be overwritten in step 7 and Windows bootloader will once again take control of loading your OS(s).

Related questions as above - >

Question - How do I fix my laptop when it shows error: no such partition and grub rescue?
Or
I have deleted Linux partition through Disk manager by selecting unidentified volume on my Windows. Now when I started my laptop again, it shows error: no such partition, entering grub rescue mode. What should I do now?
Solution

Method-1
-Stop panicking, you didnt loose your data.
-Switch on the laptop, wait till you get the Grub Rescue Screen.
-Type the following commands
ls
It will show you a list of partions you have made.
You will get something like this (hd0),(hd0,msdos1)(hd0,msdos2)(hd0,msdos4)
You need to find which drive is your Ubuntu root for which type the following:

set prefix= (hd0,msdos1)/boot/grub

If its not the root drive you will get an error message "unknown filesystem".
In that case try the same command with the next partion, ex:set prefix=(hd0,msdos2)/boot/grub
If you are not getting an error, congrats you have found your root drive. You can proceed to the next command after that:
set prefix=(hd0,msdos1)/boot/grub
insmod normal
normal
Your Pc will now boot successfully, now select Ubuntu & login.
Open Terminal( Ctr+Alt+T or use the search)
sudo update-grub
sudo grub-install/dev/sda
Now the bootloader error is fixed you should be able to boot your laptop normally & even your data is intact.

If sudo update-grub didn't work type sudo grub-updat

Method - 2

If above method is not working then you need to use this method and this will work 100%.
If you don't want to lose your data of window os then this method is specially for you.
I guess you know about fedora OS which is a type of Linux OS you just use that on your computer /laptop.
You know you just deleted a path of your Ubuntu OS or any other Linux OS that's not matter here matter is that you deleted a path of partition so you need to create a new path and for that fedora is better than the Ubuntu.
When I faced this problem first I tried to make path with Ubuntu but that was erasing my window and window data so I didn't use Ubuntu.
I used fedora and I created a new partition with Window 8.1
So in my opinion this is better way to keep your data safe.