Hi Ken,
this will probably require higher powers (read: Moe) than my very limited ones... in the meantime here's what comes to my mind:
[1] You have probably already tried this, but just in case: When running from a live system/usb stick can you mount/unmount your new partition (#4 I assume) under GParted's "Partition" menu?
[2] If no to [1]: Can you have GParted run a check on that partition (also under Partition menu in GParted)?
[3] Primary vs extended partition: not necessarily odd in itself; "traditional" hard disks allow a maximum of 4 partitions. The extended partition is simply a workaround to get past that limit, by allowing to have more "logical partitions" under the extended one. The fact that it was grayed out though in GParted does seem a bit odd. Assuming you have no data in your extended partition, can you run GParted from a live system/usb stick and delete the extended partition (only 2GB anyway)? Then see if that changes anything about accessibility of your new partition.
[4] To allow Moe to wield his full diagnostic powers it might be helpful to post the output to the following commands back t this thread (while running from your hard disk rather than the live system):
Code:
sudo fdisk -l -u
(lists logical names for the partitions)
Code:
sudo blkid
(UUID identifiers for partitions)
Code:
cat /etc/mstab
(what's currently mounted)
Code:
cat /etc/fstab
(what your system tries to mount when starting up)