I am trying to install ubuntu 12.04 using WUBI.exe from within windows 7. All goes well but when it restarts and installation proceeds it gives and error "No root file system defined". I have tried booting from live USB and Live CD but the same error occurs. Then i downloaded 11.10 version and booted into it using live USB but same error occurs there.

Now the thing is that i have 4 partitions on hard disk: 1- C: 147GB (with WINDOWS 7 installed) 2- D, E which i use for file storage in windows 3- G: 19GB NTFS formatted from windows I am trying to install Ubuntu into this G drive. I want to keep my windows 7 files and installation intact. I have tried it a while ago for 11.10 and at that time it all went super smooth. I have tried rebuilding the partition table from cmd.exe in windows and i have also tried by formating my G drive to ext3 using Easeus Partition manager in windows and then installing using wubi but wubi.exe didn't detected the partition formated to ext3. When i ran the installation wizard from within ubuntu running through live usb, i got a window with DEVICE= /dev/sda and no type no size nothing.

here when i choose my 320GB drive it just gives the option as in picture and when i pressed install the same error "no root file system defined". I have tried to select the new partition table option but it give me the window to create a partition by dividing 320GB whole into whatever i want. I don't proceed into that option because i think i will ruin my windows 7 stuff.

i am posting the pictures at of installation steps i have defined in the following link please have a look.
https://www.sugarsync.com/pf/D0690308_082_7483607
https://www.sugarsync.com/pf/D0690308_082_7483603

Please help me!

You must allocate a free space and specify at least root partition. Use button "add", create partition and assign it to "/" (it's called root partition).

Boot to your Live CD and open a terminal and post the results of this command;
I suspect that your problem is that the installer is trying to create a / (root) partition to install Ubuntu on and a /swap partition. This would give you 5 primary partitions. You can only have 4 primary partitions.

You need to use the tool "gparted" in the live session to format your free space to be an "extended" partition if this is the case. An extended partition is a type of primary partition that can have "logical" partitions created with in it. I have, for instance, 9 partitions on my sdb drive with no problem with room for more.

You would end up with 3 primary partitions, 1 extended partition with one ext3 (4 is better but I don't know if MS will deal with it) and one linux swap logical partitions with in it.

You could probably get the auto installer to install on the extended partition. It should create the two partitions you need.

I do not recommend this however. I would use the manual partitioning option which I believe that Ubuntu calls "something else". Using gparted to make your partitions ahead of time you can then point the installer to the correct partition with more confidence that it will not eat your other partitions.

All this is conjecture from your post. Give the out put from the command above before doing anything.

When you use WUBI to install, you have absolutely no need to change your partitioning. WUBI creates a large Windows file that becomes the entire Ubuntu hard disk, and then installs within that file. For 12.04, using a 19-GB area will be making it very tight. If you still want to use your G: drive, format it back to NTFS and then select it in the WUBI installer; the installer will create the necessary file and format that "virtual disk" to ext4, then install 12.04 into that space. When installation is complete, your 12.04 system will contain an additional directory named "/host" which gives access to the Windows drive on which it is installed. If you want to access your C: drive's files from inside 12.04, you need to put the WUBI installation on C: rather than G: though. Since it's just another file to Windows, it will not interfere with your Win7 system.

I have a somewhat similar installation on my laptop, which has two Windows drives. I told WUBI to create a 20-GB installation on D: and everything just worked.

Hope this helps some! The entire reason for WUBI's existence is to avoid any need for changing partitions.

here is the output of that command

Disk /dev/sda: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625142448 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: 0xc8000000

Device Boot Start End Blocks Id System
/dev/sda1 63 144584 72261 de Dell Utility
/dev/sda2 * 31602688 340178935 154288124 7 HPFS/NTFS/exFAT
/dev/sda3 585264078 625137344 19936633+ 7 HPFS/NTFS/exFAT
/dev/sda4 144586 585254311 292554863 f W95 Ext'd (LBA)
/dev/sda5 144649 31599854 15727603 7 HPFS/NTFS/exFAT
/dev/sda6 340192503 482769314 71288406 7 HPFS/NTFS/exFAT
/dev/sda7 482772992 585254311 51240660 7 HPFS/NTFS/exFAT

Partition table entries are not in disk order

Disk /dev/sdb: 8046 MB, 8046772224 bytes
255 heads, 63 sectors/track, 978 cylinders, total 15716352 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: 0x5027e4e6

Device Boot Start End Blocks Id System
/dev/sdb1 * 63 15716351 7858144+ b W95 FAT32

Disk /dev/sdc: 125 MB, 125698048 bytes
8 heads, 32 sectors/track, 959 cylinders, total 245504 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: 0x02ab3556

Device Boot Start End Blocks Id System
/dev/sdc1 99 245503 122702+ 6 FAT16