I recently installed a second hard drive on a Windows XP computer. I installed Ubuntu 12.04 from DVD-ROM onto the second drive, using the installer to partition. When I start the computer, I do not get the option to choose the operating system, and Windows shows the drive (F:) as not having any Linux files. What is my next step?
This may answer your question; however, there could be a variety of problems with this, but I hope I'll find the solution for you.
First, whenever you boot, hold down both Shift keys as soon as your computer hits the BIOS screen. Normally the Left one is necessary, but both won't hurt. :) What this does is, if it is configured already, will display the GRUB selection menu. GRUB, or the GRand Universal Bootloader, will list both Ubuntu and Windows booting options. If this doesn't work, read on.
The problem may be that the partition with GRUB on is not being booted, but the Windows one is. Boot from your Ubuntu DVD/CD/USB and select "Try Without Installing". Now, open up terminal from the Unity dash. Run the following commands:
Then, with the Dash, open up Grub Customizer. Now, click on Preferences on the top right corner. Now, look for default entry and select the Ubuntu partition (Not recovery). Click close, Save, and close the application. Now, reboot. It should now load GRUB.
Edit: This solution is for if you have Ubuntu installed on a separate partition; it may work for separate hard drives, however. I do not know from experience if this works for multiple drives, but I know that it works for separate partitions on ONE drive.