My old laptop had a similar probLEm to what Chavdar recounted: its
USB ports didn't emit quite enough juice for my partner's USB hard
drive (it would just make a ticking noise).  We ended up purchasing
a powered hub which did the trick.  I can't test it right now,
but I'm 95% certain that the symptoms were as you described.

Brian.

-- 
  Brian de Alwis | Software Practices Lab | UBC | http://www.cs.ubc.ca/~bsd/
      "Amusement to an observing mind is study." - Benjamin Disraeli