I installed ubuntu 11.04 alongside windows 7 on a partition that previously had ubuntu 10.04. It installed perfectly but on completion, after the reboot, the boot menu shows just 'memtest' and windows 7 as options - no option for loading ubuntu.
migrated from stackoverflow.com Jul 22 '11 at 21:37
(I expect this question will be moved to Ask Ubuntu, but I'll throw this answer on while we wait).
First, boot to a live cd to make sure your installed Ubuntu partition is still there (I fully expect it to be).
Second, (assuming the 1st step showed you that you still have an Ubuntu install) look at your partition table and your grub.conf file - make sure it's the grub.conf file of your installed system, not the live cd :) You may just have to manually write in the line for your Ubuntu partition. It's odd that the generated grub.conf file would be broken.
On the bootloader, type "c". Then type:
In case you have more than one hard drives, you could have installed the new bootloader on the other (or one of the others, if you have more than two) drive. Changing the boot device priority can grant you access to that bootloader.
If that is not the problem, you should try restoring grub following this tutorial http://ubuntuguide.net/how-to-restore-grub-2-after-reinstalling-windows-xpvistawin7
(i know that its title says "after installing windows" but , of course, the steps used there are just as good for reinstalling grub after any problem)
If you've got a live CD, you can try the following command out in the terminal after choosing Trying Ubuntu:
sudo apt-get install grub //firstly install grub
if you load into the grub prompt
kernel /boot/vmlinuz--generic ro root=/dev/sda7 //sda7=(hd0,6), replace it with your own
no need to remember the kernel version, just use tab to help you
I've just done this to dual boot my win7 (on sda1) and ubuntu 11.04 (on sda5)
Well, without the Live CD try to search for grub4dos to boot ubuntu with the windows bootloader