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.