Can't Get Anywhere on my Computer!! I have Finals in a Week!!!

Ah, there's the problem. That's not your startup disk. That's the recovery partition. You want to create an image from what will probably be called "Macintosh HD", which will usually be the second option in the list. Depending on how many documents and pictures you have, it should be no less than 20GB in size at the bare minimum, and is likely much larger. This will take more than five minutes to do. Take a look at the screenshot for additional information.

In the meantime, I will get some sleep. It is 1:40 in the morning over here. Let me know what happens.

I thought that might happen. Looks like you will need to partition the external drive, and restore the startup disk to the partition on the external drive. The only hiccup in this process may be the actual partitioning of the external drive. Depending on what format the external drive is, you may not be able to modify the partitions without deleting the current partition. It will tell you if you are unable to simply resize the partitions. Look for something similar to what is in the red box in the image below. Also, if you can resize the partitions, the + won't be grayed out, and you will be able to drag the divider between the partitions (represented as white boxes on the left) in order to resize them.

Make sure that you make the partition big enough to hold the startup disk ("Macintosh HD"). An example size can be seen in the red box in the image below. I'd give it at least a 5GB cushion.

Once you do that/if this doesn't work, go ahead and attempt to turn off the encryption on the disk. You can find that under the File menu, as shown below. Enter your password when necessary, and if it's grayed out, you may need to unlock it first, as detailed above.

Hopefully this can resolve your issue. If not, I strongly recommend taking it in to the nearest Certified Repair shop.

Wether you did it or not I think you have FileVault enabled. What I mean is if you installed Yosemite from the app store it may have got enabled during the install. I would try booting by going to safe mode. Hold the shift key down at startup. And if you can ,go to system preferences security- FileVault and disable it. It will ask for a password which should be the same as your administrator password or your apple id password. If you cannot do this. Post back as you will have to go to recovery and use terminal.

Master Boot Partition is for windows operating systems. Mac in oS X use GUID.

If the external hard drive was formatted with an MBR, then you may need to use Disk Management on a Windows machine to create a partition or block off free space first.

I know I'm answering your older post, but as I now know the external drive is Master Boot Record, I can tell you that you can read the drive but not write to it in Mac.

You will have to go to recovery and use terminal to turn it off. Here is a link that tells you the commands to see if it's on and to turn it off. http://www.mactricksandtips.com/2014/01/check-enable-and-disable-filevault-from- terminal.