WD AV-GP 2 TB AV, WD20EURS Doesn't Show Up in MyComputer or Disk Management

When I turned on my pc this morning, the hdds were in MyComputer and Disk Management.  I was able to change them from Dynamic to Basic and assign them drive letters.  I don’t know what the difference was between rebooting several times yesterday and booting up this morning so I found no reason why they available this morning.  But I thought I’d let people know.