Why won't my PC boot ?

[Cyclops]

I've just fitted an external hard drive. It all works fine apart from my PC won't boot with the drive connected. If I unplug the external drive it all boots up OK then I reconnect the drive and everything works fine.

I'm running Windoze XP and the drive connects via USB 2.

[alecstilleyedye]

is there a system preference for which disk it boots from? if it's set by default to an external device (that has no system software on it), that could cause the problem. macs can specify which device, but if they can't find system software on it, they will boot from the internal hard drive anyway.

[Valiant]

Check your BIOS for boot up sequence.

[border-rider]

Yep

It's very likely that the boot sequence is set so that the USB device has priority.  That's actually quite useful, sometimes.  You'll see instructions on how to access the BIOS settings as the machine boots up - it involves holding diwn one of the F keys as it boots, then a few pages of menu options will open - once you get that far it's pretty straightforward to navigate to the page with the boot sequence on it and move the USB device down below the hard drive

But be careful - if you ever need to boot from a USB stick or a USB CD (for data recovery or  to reinstall an OS for example) you'll have to change it back.

[Cyclops]

Solved the problem - in the BIOS the external drive had replaced the internal as the first HDD and so the PC wasn't trying to boot from the internal drive at all.

Thanks all