The TomTom GO910 is a wonderful satnav and can be obtained very cheaply on e-bay faulty.
The main fault with these is they contain a 20gb harddrive that is prone to failing and are expensive to replace.
The Go910 only needs less than 1gb of space for the maps and the rest is for storage of music.
The easiest and cheapest way to repair these is as follows.
1..Remove the faulty harddrive from the unit.
2..install a Zip to CF adaptor (available on ebay for a couple of pounds)
3..Install a CF card of your choice.
4..re-assemble sat nav.
5..connect to the tomtom software and let tom tom reload the operating system and maps.
This may also work with the go710