We have a new Dell Optiplex 790 desktop with Windows 7 and just installed Ubuntu 12.04 on it using a USB stick that was configured as a boot drive. We created a new partition for Ubuntu during installation using the partition editor that comes up during installation.

Everything seems to have gone fine with the installation except that, unexpectedly, there is no option to boot up Ubuntu when the computer is started. We just start the computer and Windows starts up with no option to ever start Ubuntu.

The only way we have gotten Ubuntu to start is by putting the USB stick used for installation back into the computer and having the computer boot from it. Then GRUB shows up and the Ubuntu OS that we installed starts up (rather than the live-CD version on the USB stick).

Previous times we have installed Ubuntu, GRUB shows up when we start the computer and we can choose among the various OSes installed.

Can anyone suggest what to do? We want to have the option to launch either Windows 7 or Ubuntu 12.04 when we start the computer, with the default being Windows 7. Right now there is no option and Windows 7 just starts the way it did before we installed Ubuntu.

Note that if we hit F1 soon after starting the computer, we get some sort of Windows bootloader (not sure of exact name) but there is no option for Ubuntu; just Windows 7. Also note that if we hit the shift key soon after starting the computer, as some help pages have suggested, nothing happens (Windows 7 is loaded as usual).

Thanks in advance!