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I have a HP Probook 4525s laptop with Windows 7 and Ubuntu installed on it and an external USB Toshiba hard disk(320GB); I've tried to install for several times various linux distros on the USB HD (Ubuntu, Backtrack, Suse 11, Scientific Linux) but I have problems booting it. The instalation went well but, when it comes to boot the external HD, everything stops to a dash blinking forever on a black background. I've tried changing the boot order and manually select the booting device but doesn't solve the problem. If I remove the external HD when the dash blinks, the laptop boots the internal HD and I get the ubuntu boot menu. I've tried booting from other computers and everything works fine, so it seems that my machine has a problem.

What should I do in this case? Any suggestion may be useful.

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Sorry, but this isn't really a Linux problem then, but a hardware/BIOS issue. You will need to figure out how to make your computer boot from USB. Maybe a BIOS update will do the trick? You could always contact the manufacturer for support. – Martin von Wittich Sep 25 '13 at 21:55
The 'dash blinking forever' tends to indicate a grub problem. Most likely, when you installed <insert_your_distro_name_here>, grub was being installed to your external hard disk. Re-installing grub should correct the problem. – Timothy Martin Sep 25 '13 at 22:55

Try adding grub entry in internal HDD's grub.conf file for external HDD.

Don't forget to append rootdelay=7 in kernel line

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Try another bootloader, e.g. LILO, Syslinux or check the list on Wikipedia for inspiration. LILO and SYSLINUX have the advantage of being usually packaged in distributions.

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