Technically, running a hard drive, keyboard and mouse should all be possible. However with the root file system on the USB hard drive it is conceivable that there is to much traffic across the bus and the mouse and keyboard are not being detected properly. Usually this happens when running silly-massive amounts of data like 4 printers and 6 web cams. The hard drive should not be transferring that much, but it is possible.
All that said, you are in should work land so...
- Make sure your using a powered USB hub (not direct to computer, or unpowered hub). A hard drive can require a lot of power, specially if it's the kind that draws it's power from usb.
- Try to use different "controllers" for the hard drive and the input devices. On a laptop that can be kind of tricky, and you really just need to move the connections around.
- Unplug the mouse, then run
tail -f /var/log/syslog plug the mouse in, watch for errors. If nothing happens at all, you likely have a hardware issue (either real, or you just have "too much" happening on that bus and the BIOS isn't passing up events/data.) If something does show up you should get a error message that tells you why it isn't working.
- Try running
lsusb and see if your devices are listed. If they are they should be working, if not, then you have a kernel (or hardware) level problem.
- Try a live CD. Do they work there? If so, your down to your configuration, if not, then your back to hardware or unsupported devices.