Re: Cannot install Ubuntu 12.04 in Dell XPS 14 ultrabook
I just finished installing 12.04 on my daughters' two brand-new Inspiron 14z laptops and had a real problem trying to do so, which sounds similar to your situation.
In my case, it turned out that the hard drives had some kind of RAID enabled which prevented Ubiquity from seeing the partition table.
The solution for me was to open a terminal as I was "trying out" 12.04 and type in the following command:
sudo dmraid -rE /dev/sda
Then, I could click on "Install 12.04" and away we went.
This is documented in a number of places, the best of which is the discussion at: