I found the solution elsewhere on the fourm. It is listed below. It was a bit scary installing an update to my chipset but it worked perfectly. My 3TB disc is now showing capacity at 2.72TB. Much better that the 746GB before the fix.
Re: Windows 7 64-bit won’t show full size 3TB of WD30EZRX
If you have Intel chipset you have to download lates version of chipset.
My chipset is Intel Q57
In my case helped newest chipset version 10.6.0.1022
http://downloadcenter.intel.com/Detail_Desc.aspx?ProductID=2101&DwnldID=20215&lang=eng&iid=dc_rss
