hi,
My scanner (Canon LiDE 25) started to misbehave one day - when the PC would be turned on, and the scanner would start and then scan (nothing!) until the scanning arm got to the end of the flatbed and then wouldn't stop... it just kept making this nasty mechanical noise, and in the end it would have to be unplugged. Unplugging it and then plugging it back in again a few times seemed to solve the problem. When the scanning arm settled at the origin of the flatbed and STOPPED, it would be obvious that the problem was sorted for that iteration of unplugging and plugging.
This problem has gone on for some time now. Funnily enough, and as a side comment, my previous scanner (the one that I threw away because I thought it was broken) demonstrated exactly the same problem. So, I buy a new scanner, and lo and behold it starts doing the same thing.
Then... one day, I realised what the problem was. My scanner has been plugged into a high speed USB 2 hub, and so have a number of other devices (external hard drive, printer etc).. and one day I decided to plug it DIRECTLY into the USB port of the PC (rather than into the hub)... and I can't reproduce the problem, at all.
When presenting Canon with this problem, they blamed the Operating System and said that extraneous commands were coming from the OS to start the scanning process. My suggestion is that it just doesn't like being plugged into a hub (not quite sure why - you'd have to ask a hardware engineer that).
Good luck... and happy scanning.
Michael Haig.