From the screenshot,it was clearly shown that you installed Windows on a logical partition.Windows doesn't boot from a logical partition,it only boots from a primary partition.

So delete /dev/sda8 and install windows on a primary partition other than extended partition.

For this,follow the below steps.

1. Boot ubuntu-live-disk(so that your ubuntu partition will be unmounted and you will be able to resize it) and install gparted by running the below commands on terminal,

   
   
   

   sudo apt-get update
   
   sudo apt-get install gparted && sudo gparted
   
   




2. Right click on the /dev/sda8 ntfs partition and delete it by selecting delete option.




3. Now the unallocated spaces before and after /dev/sda8 combine into one.(unallocated space= 3.74 MB+100.09 GB+4.74MB).




4. Then you have to move the total unallocated space,just below to the /dev/sda7 linux-swap partition,so that the total unallocated space will be throw out of the extended partition.For this,




5. Right click on the dev/sda6 and select Resize/Move option.Click on the slider and move it to the left atmost.




6. Now the unallocated space comes just below to the /dev/sda6.

   
   
   

   




7. Try the same like i did on step 5 to move the unallocated space just below to the /dev/sda7 linux swap partition.




8. Now the total unallocated space of about 100 GB are comes at the last of the extended partition.Now right-click on the extended partition and click on the Resize/Move option then you can be able to shrink or shorten the extended partition to throw 100 GB unallocated space out of the extended partition.




9. Right click on the unallocated space just below to the extended partition and select New option.




10. From that create a new primary ntfs partition.And then install Windows os on it.