Hi there,
are the two unseen drives new? If yes, go to Control Panel/System and Security/Administrative Tools/Create and Format Hard Partitions. You will need to initialise and format the drives for them to be seen in Windows 7
If they are old drives that have already been formatted, go into BIOS and check under the System Heading for ATA Port Information. Highlight this then double click or press enter key on keyboard to bring up sub-menu and check that the SATA ports are enabled. If you plan to Hot-Plug any HDD's then you also set this here.