Ubuntu – “This computer currently has no detected operating systems” when installing

I am new to Ubuntu (AMD64) and am attempting to install it on my laptop which already has Windows 7 Home Premium x64.

I currently have two partitions on my HDD and I was planning on repartitioning my secondary partition to make room for a third to use for Ubuntu. However when I attempt to install I get the following message:

"This computer currently has no detected operating systems"

Choosing "something else" takes me to the partitions. However, it only detects a single unpartitioned space (my entire HDD) even though I actually have 2 partitions taking up plenty of space.

By no means can I detect my two partitions using any method.
Is it possible the 32 bit installation might be more successful? (I doubt it but I had to ask)

Edit:
250gb. I have two partitions for windows (one main and another for storage) as well as an empty third partition with 20gb that I intend to use for Ubuntu. None are detected, however.

FINAL EDIT:
I finally fixed the problem. when I ran

sudo fdisk -l

it gave me several partitions in the list, so I tried running fixparts on individual partitions, which ended up being inconclusive (and confusing)

Then I decided to try to run fixparts over the entire unpartitioned space

sudo fixparts /dev/sda

AS OPPOSED TO

sudo fixparts /dev/sda1

sudo fixparts /dev/sda2

(individual partitions) and so on.

After simply running the command on the entire hdd, it quickly finished and alas it was fixed! Going back to the installation, it detected my Windows 7 installation, and also detected all existing partitions in the custom install mode. Furthermore, my data on my other partitions was left completely unscathed. It fixed my problem at no cost.