I had Ubuntu 11.10 installed, I installed Windows 7 on another partition but now on booting I cant see dual boot options and Windows 7 is loaded.
How can I run Ubuntu now?
Your grub2 installation was removed from the MBR by the Windows installation.
Please follow the instructions in the Recovering Ubuntu After Installing Windows wiki page, the graphical method should restore your grub2 install that was over written by the Windows installation.
- Insert your Ubuntu CD, reboot your computer and set it to boot from CD in the BIOS and boot into a live session. You can also use a LiveUSB if you have created one in the past.
- Install and run Boot-Repair
- After this, click "Recommended repair" and apply. If you are willing to use the advanced options, make sure you leave the "Reinstall GRUB" checkbox ticked. Now reboot your system. The usual GRUB boot menu should appear. If it does not, hold Left Shift while booting. You will be able to choose between Ubuntu and Windows.
The recovery method should detect both your new Windows and the Ubuntu install.
Is seems you have to reinstall grub as it was wiped after installing Windows 7. If I'm correct you will be looking for reinstalling grub 2. There seems to be some options for restoring grub 2 given on the ubuntu community help site: https://help.ubuntu.com/community/Grub2#Reinstalling_GRUB2
Re install GRUB. If you have a Ubuntu Live CD and you know the partition where Ubuntu is installed, then this blog post will help you for sure :-)
Windows 7 has its own boot manager which boots Windows, so when you install Windows 7 grub isn't avaible to load both operative systems, to solve this i'd use http://www.supergrubdisk.org/ , then you'll be able to get in ubuntu, upgrade your grub:
sudo update-grub and this should fix your problem-