Modern devices such as your nuvi 2589 are notoriously difficult to get into preboot, anecdotally C4 devices seem to be the most difficult. I don't have one available to confirm however it is likely pressure on top LH corner while powering on. When they do enter preboot they stay in it for a very short time and you need to be a sniper to hit 'OK' on Updater's GUI quick enough. It helps to power on by plugging into the PC rather than using the power button and then connecting the USB cable. If you do use the latter method it's likely too late to catch preboot. Read this [Only registered and activated users can see links. ] Regardless, you shouldn't need to access preboot, is there a reason you wanted to do so?

You can get many files back safely using GarminExpress. It may not give you everything, the basemap for instance as i mentioned earlier. It's unlikely it's a corrupt file so you can take a copy of the one in your backup or get one here: [Only registered and activated users can see links. ]. Be very careful what you use from your backup in case you restore a corrupt file. Replace the detail map (LM entitlement) with GE.