Please read my thread Common Installation Problems and Their Solutions
Problem: Error message “Setup was unable to create a new system partition or locate an existing system partition.” What to try:
Make sure that the partition is primary, active, and formatted with NTFS. Instructions for marking a partition as active using Diskpart:
Open an elevated command prompt: Method 1: From Windows
Click on Start and type “command prompt”
Right-click on the application and select “Run as administrator”
Choose “Yes” when asked to confirm Method 2: From a Windows install/repair disc
Boot into the install/repair disc and wait for it to load
Choose “Repair my computer”
Select “Command Prompt”
and press enter.
Enter list disk
and note the number of the disk you want to install on.
Enter select disk n
n is the number of the disk.
Enter list partition
and note the number of the partition you want to install on.
Enter select partition n
n is the number of the partition.
You can now close the command prompt and re-attempt installation.