Did you just recently install win8? It didn't put the OS on that drive, it put the boot loader on that drive. The drive needs partitioned as GPT not MBR. You will need to delete the partitions and recreate as GPT. In doing so, you'll probably lose the ability to start windows. To test this out, shut down your computer. Disconnect the power from the 3TB drive, now see if you can boot. If you can't, install the win8 install disc and try to do a repair install. This should move the boot loader to the OS disk. Now reconnect power to the 3TB disk and see if you can delete the partitions and create new ones.
Wondering if you can help me - Specs: Win7 Ultimate installed on SSD - starts up fully with SSD. I installed 3TB Seagate 7200 for more storage but Disk Management only recognizes 2048.00 GB, with the remaining 746.52GB unallocated and all the options grayed out. I've formatted the entire disk with Seagate DiscWizard, and it says the extended capacity manager is recognizing the additional space, but the Disk Management disagreed. The 2TB portion is shown as the G: drive. I can't get the remaining 746GB to be allocated, formatted or recognized.
System specs are:
AMD Athlon 64 X2 Dual-Core 5000+