error: no such partition.
grub rescue>

I was running Windows7 and installed Ubuntu Desktop 12.04 LTS as a dual boot system. This is what I did...

First, I downloaded Ubuntu and the installer file to a thumb drive and installed it from the boot menu. Near the end of the process it asked me to set the partition size and I left it the way it was presented. When I restarted the session, it didn't seem to take. I couldn't access Ubuntu but through the thumb drive. So, I installed it again.

This time when it asked me to set the partition size the available space was smaller. So I concluded that it took the first install. Again, I left the setting for the partition alone. This time it worked when I restarted it and was using Ubuntu for a couple days, on a dual boot system.

Knowing that I installed it twice and there were two different partitions with the same OS, I went into Windows Disk Manager and deleted what I thought was the partition with the extra OS. When I restarted I got this message:

error: no such partition.
grub rescue>

Can I recover my old OS's? Or do I need to reinstall both? It won't accept the USB, it gives me the same message.

I am surprised that you didn't determine for certain which partition Ubuntu was on before you deleted one.
I would use the Disk Manager to delete the other ubuntu partition that you did not already delete, and then use all the unused space to create a bigger partition to install Ubuntu on.

It should be pretty easy to recover everything (if Ubuntu is actually still there), but you have to get that USB (or CD or whatever) booting.
Go carefully through the BIOS options to see if you can get it to work, then post back.

syg00 is correct that the first step is to get it booting.
if grub rescue gave you the message "no such partition", is it possible that you installed grub to the partition that you deleted instead of installing grub to the MBR?
In that case, all you would have to do is reinstall grub.
When you say
please make sure that you have it set to boot off the USB, not the hard drive.

When you installed it the second time you should have replaced the first install. What you did is changed the partition count by deleting that partition (or you actually deleted the partition where grub was, hard to say), which is why you're getting the error, but I suspect it's the first case. You should be able to reinstal grub and get it working again.

It's possible that the OP erased the first installation which means like guyonearth said partition count changed & also /etc/fstab. You can go thru grub rescue prompt get it booted & change the /etc/fstab, then update-grub.
http://karuppuswamy.com/wordpress/20...-cd-for-grub2/

EDDY1, the link that you posted seems to apply, although I'm not sure what my hard disk #'s were or my partition numbers. I think that Windows7 was on sda3 and sda4. When I type ls in response to the grub rescue> prompt, this what I get:

grub rescue> ls
(hd0) (hd0,msdos5) (hd0,msdos4) (hd0,msdos2) (hd0,msdos1)

and that's all I get and that's all I can make it do. So I don't want to enter the wrong partition number and screw it up even more. Though, I am pretty sure Windows7 is on sda3 and sda4, and I could boot fully from either one.

You are getting the grub error because the partition you deleted was the default operating system, and that is where the grub config files were. Now it does not boot because it can't find the config files.
All you have to do is reinstall grub.

"You can get grub to list partitions using "ls"
http://www.gnu.org/software/grub/man...cue-shell.html

EDDY1,
As you can see from the quote you listed, I used ls to list the partitions. But how do I determine which of those partitions to use?

Can you somehow give us the list of partitions even if you have to write it down manually?

So I'm guessing here but I think I must've deleted the partition containing grub or the mbr.

Not necessarily true, if you erase partitions within the logical/extended partitions that are before your linux installation then the partition #'s within the logical change, which affects your fstab.
If you boot the right partition then you can correct your fstab after boot.

Did you already boot in your liveCD or USB and run fdisk -l on terminal? that will tell you what partition is controlling the booting of your OS.

you can identify the partition because it usually has a * next to it.

Good luck to you!

will list partitions at grub prompt