"This computer currently has no detected operating systems" when installing [duplicate]

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.

I had a similar problem where somehow I had two conflicting partition tables. I used the livecd and then used a utility called fixparts which sorted the problem out. Details here: http://www.rodsbooks.com/fixparts/.

This was most helpful.

I didn't know which option to choose after entering

sudo fixparts /dev/sda

but I found the answer 'w' here: Ubuntu 13.04 not detecting Windows 7 during Install

I've installed ubuntu alongside windows several times, but I've never run into the "missing dual-boot option" before.

The solution took quite a bit of searching to find.

If this is a new problem, due to some recent modification of Windows 7, perhaps your way to handle it should be posted in a more prominent site, (eg in the ubuntu download site).

Thanks again for the solution.