I just built my pc yesterday and I'm encountering little problems here and there. I've got one that I can't figure out here. My hard drive has about 750 inaccessible GBs. It's a 3TB drive and my storage says 2 TB available. I'm not sure how to work around this, as I cannot select new simple volume. Here's a pic of my problem

http://imgur.com/a/xVkP1Rite clik it and select Allocate...then format it I think yu should leave it alone until yu know why or how it got that way.
What is the name and model of the HDD?

EDIT: This is a know behaviour of Windows 8.
https://www.eightforums.com/installation-setup/50491-formatting-3tb-hdd-windows-8-1-pro-install.html

Also, Seagate has documented this issue elsewhere.
http://knowledge.seagate.com/articles/en_US/FAQ/218619en
Quote

Most LEGACY systems built before 2011 have a traditional PC BIOS. This type of BIOS uses a Master Boot Record (MBR). The MBR Partitions can define a disk drive capacity up to 2.2TB. Windows operating systems that boot from an MBR are therefore limited to 2.2TB per MBR. A 3TB disk drive in a legacy BIOS and Window system will need a DiscWizard device driver to access the full capacity of a 3TB disk drive. Two partitions will be necessary because of the MBR limitation. The device driver mounts the capacity above 2.2TB with another MBR which looks to the system as a second virtual “PHYSICAL” device.

GUID Partition Tables (GPT) can define drives larger than 2.2TB. You can use GPT today on any Windows 10/ 8.1/8/7 and Vista system as a non-booting data drive. Windows can only boot a GPT partition on a new type of BIOS called UEFI.

UEFI BIOS desktop systems are new since 2011. Windows 10/8/8.1/7 64-bit and Vista 64-bit operating systems support booting from UEFI and GPT WITHOUT the need of a non-Microsoft device driver. This is the Windows native SOLUTION for booting a 3TB drive to a single partition.