I was having Ubuntu 16.04 alongside Windows 10 and having dual boot and everything was just fine. I deleted the partition of Ubuntu 16.04 from Disk Management in Windows in order to install 18.04 on it and it just happened during the installation progress.
Now from the Disk Managment there are 5GB used in this partition and I think that 18.04 is installed but I can't access it and my PC boots directly into Windows.
What you've done is a mistake. But a solution is available.
How come you delete the Ubuntu partition from Windows when you're on a dual boot?
GRUB is the bootloader and it is contained in the partition alongside Ubuntu. GRUB helps you load your Operating System. Without the bootloader, how come you come load the Operating System now?
Solution:
There is absolutely no loss of data from Windows.
You need a bootable DVD/Pendrive containing your version of Windows. Say, you have Windows 10 Pro on your PC, you need a boot Disk/Pendrive containing Windows 10 Pro; If it's Windows 7 Professional, you need a drive containing Windows 7 Professional.
Plug it, restart your PC and enter boot mode. Select Repair Windows... option and open Command Prompt. In the CMD, type the below commands:
bootrec.exe /fixbootbootrec.exe /fixmbrThis would fix everything. Years ago, I've come across the same problem.
Now, you can log in into Windows as you did earlier. Go ahead and download Ubuntu 18.04 and dual boot your PC.
The history of how you nuked 16.04 and 18.04 is only partially installed is unimportant at this stage.
You need to follow the instructions in:
Make notes as you go along. If you encounter a problem installing 18.04 post a new question with exact details.
You need to consider that 18.04 was just released and it might have a problem operating on your system. You may wish to install 16.04 again instead.
If you choose to install Ubuntu 16.04 again you can still try 18.04 on a new test partition. This is better than erasing 16.04 and installing 18.04 fresh (which didn't work in your case). You can also clone your 16.04 data to a new test partition and upgrade to 18.04 on the clone:
This way you can keep cloning and testing 18.04 upgrade until weeks or months have passed. Keep monitoring when Ubuntu bug fixes are released that affect your system. Then test them and other areas until you are satisfied Ubuntu 18.04 works properly for you.
