First, unallocated space in a partitioning tool like GParted is different from unused space on a partition. Unallocated space in the partition table is unusable from an OS unless and until a partition is created in that space, or until an existing partition is resized to cover that space. This is because a partition is sort of like a room number in a hotel; without it, although the space exists on the disk(/hotel), the OS(/guest) can't locate it.

Second, you should never create a partition in Windows that you intend to be used by Linux. You seem to have gotten lucky and didn't do any damage, but many people who do what you did end up having to use third-party utilities to fix the damage -- when asked to create more than four partitions, Windows will, unbidden, convert from a standard partitioning setup to a Logical Disk Manager (LDM), aka dynamic disks, setup. You can't install Linux to such a disk, so you've got to undo this operation, which of course can't be done with the tools that Microsoft provides.

If you intended to install Linux to one of your existing partitions, then I recommend you:

1. Delete that partition.


2. Move/resize your remaining partitions so that they're contiguous. If you move /dev/sda4, do so from Windows; if you do it from Linux, Windows will probably stop booting.


3. Reboot to Ubuntu (or any Linux emergency system).


4. Create an extended partition in the unallocated space and create logical partitions inside that extended partition for Linux's use.


5. Install Ubuntu to the logical partition(s) you've created.

If, OTOH, all four of your existing partitions are in use by Windows, you could do the same as I've just described, but for step #1, delete a partition that you're willing to sacrifice (because it's empty or because you transfer its data to another partition). If that's not possible, try this:

1. Assuming /dev/sda4 is your Windows C: drive (it's the only one big enough to be that), move it to the end of the disk. Use Windows for this job; if you use Linux, it will probably no longer boot.


2. Assuming /dev/sda3 is not involved in the Windows boot process, convert it to a logical partition using FixParts.


3. Using GParted in Linux, resize the extended partition (which FixParts will create) to cover the space between what used to be /dev/sda3 but that will now be /dev/sda5 and /dev/sda4.


4. Install Ubuntu, and let it (or tell it to) create additional extended partitions for its own use.

Before undertaking either of these tasks, back up any important data on your disk. Partitioning operations are inherently risky, and the sorts of things you need to do run the further risk of disrupting the Windows boot process. Moving and resizing NTFS may be a little safer in Windows than in Linux. This is especially true when you're dealing with a partition that boots in BIOS mode.