My computer has 2 drives, an 30 GB SSD with Ubuntu 12.04 installed on it, and a second 500 GB HDD for storage. I've checked all my BIOS settings, and searched through Ubuntu, and I can't figure out how to access my HDD on Ubuntu.
I assume that you cannot access the secondary, 500GB drive.
Open a terminal emulator and verify that the disk is recognized by the kernel:
You'll probably see sda[0-9] and the second disk should usually be detected as sdb, but that depends on what other usb-storage devices are connected.
If the above command shows anything other that sda[0-9], try this
This will print a list of disks and/or partitions (depending on how your disks are configured) their UUIDs, file system types and labels (if applicable).
If you need more help, please paste output from those commands.