Its showing no drives are available to install to most likely because neither one is empty...
Reinstall and on that part click on the "Drive options (advanced)" option Link. From there it should show you the drives and allow you to delete the existing partitions. When you are done deleting the partitions, select it again and then click ok.
- If no drives are shown on the the "Drive options (advanced)" option, then you need to install the sata controller driver using the "Load Drivers" link on the same screen. Again, you would get these drivers from your motherbd vendors support site (or if this is pre-built, like a Dell, then from Dells support site for that model#)