Step 1 : To be safe, download Ubuntu 14.04.3 ISO again.
Step 2 : Create a proper Ubuntu USB installation media :
Open command prompt as administrator and execute :
diskpart
list disk
select disk *
clean
create partition primary
active
format fs=fat32 (quick)
assign letter=**
exit
Note : * = number of USB drive | ** = select a free drive letter
Mount the Ubuntu ISO and copy the content to the USB drive.
Step 3 : Disable hibernation mode and fast startup - execute :
powercfg /h off
Open the legacy version of the Windows Control Panel - not the modern one.
Select Power Settings - enable show hidden settings - uncheck fast startup.
After having done this - shutdown the computer completely - do NOT reboot.
Step 4 : Boot from the Ubuntu USB installation media you have created and ...
Update addressing your response that the install media still doesn't work
In case you have access to a an Ubuntu system, you can create the media by :
Open Disks and select Restore Disk Image from the menu on the top right.
Choose the Ubuntu installation ISO file and the USB drive ... start restoring.