Ah yes, I just had a closer look at the image you uploaded and it says "73.13 GB Unallocated". So naturally Windows disk management will only make a 73 GB partition if that's what it believes.
One possible reason for this: There is a setting (which is not used very often) in the firmware of a hard disk for limiting the reported available space on the HD. It's sometimes used to keep partitioning programs away from protected areas used for recovery partitions.
It would be very unusual for a 320 GB disk to be limited to 73 GB in that way but it's possible.
I read about this recently but my old brain has forgotten which utility was recommended to fix the problem. I'll do some Googling and get back to you if I find it.
Meanwhile, I recommend you download Seatools and run all its tests. It also has a "Drive Information" item which might provide some clues. It's made by Seagate but it works on other brands of hard disk too.
There is Seatools for DOS (runs from a CD or floppy) which is useful if your system can't boot, but as your problem is not with the system disk, you could use Seatools for Windows.
Seagate Technology - SeaTools
Or there is a similar hard disk diagnostics tool on the WD website, which might be better as this is a WD hard disk.
If this is a brand new disk on warranty, and you can't fix this problem easily, you could return it as faulty.