I lost my main OS when loading Ubuntu can I get it back?

Reinstall and restore your user datas from backup. You could mess around with editting partitions to be NTFS and chkdsking it but the overwritten data will be completely lost

There are data recovery companies that say they can get back data that has been overwritten, but this is tens of thousands of dollars. For all practical purposes, you data is gone from that disk.

press CTL+ALT+T to get into terminal. then type

sudo fdisk -l (that's a lower case L)

copy and post the result.

you might not have erased your old operating system. when you paste the output here, we can see if it is still there.

I have the same problem, which is why I was searching this forum. I performed the above referenced action and got this:

ubuntu@ubuntu:~$ sudo fdisk -l

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders, total 312581808 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x39633962

   Device Boot Start End Blocks Id System
/dev/sda1 2048 3074047 1536000 27 Hidden NTFS WinRE
/dev/sda2 * 3074048 312580095 154753024 83 Linux
ubuntu@ubuntu:~$

Recoverable??

it might be. i have no idea what "hidden ntfs winre" is

just go into the file manager and click through each of the entries on the left pane and look on the right pane to see if you recognize any of the directories as belong to windoze. look specifically for "program file" and "users" and files that end with .$xx and .000

if you see those, you can recover windoze.

I presume NTFS hidden is partition type n°29, which is mainly used today as Windows recovery partition. Even if it holds a NTFS file system, it's not marked as a NTFS partition. This should means Ubiquity avoid now to overwrite such partition (to be confirmed).
So you can recover your Windows OS, but except if you are ready to spend tens of hours, it means you have lost your data. As Andrew will say next, you should have done periodic backups (and an exceptional one before installation).
At boot, one of the function keys (F2, F8, F12 or another one) will allow you to boot on recovery partition to reinstall Windows. Else the bootloader could show you in boot menu a line for Windows.