Sat nav trouble, help needed please

We love the Nav510 Sat nav but last month it suddenly said insert Navigation disc. This message stayed on the screen constantly.
Having moved house we have no idea where the disc went so by chance we were lucky to buy an updated disc.
We put the disc and in the nav510.
Nothing happened. No idea if it was reading the disc or not.
To cut a long cold story short we did a soft factory reset and then a hard factory reset.
Again, we put in the navigation disc and can see the map. It seems that the map will not load into the hard drive. No sign of an "instal" prompt or a "copy to hard drive" prompt.

Any other ideas?!!

Could possibly be a dud disc ? Try a different one ? Can send you a copy of V14 that I used on my RNS510.

So, we have finally fixed our Sat nav problem.
On a recommendation we visited "Hazzy Dayz" who are VW Sat nav experts. Andy ran a diagnostic test and confirmed our suspicion that the hard drive had failed. Replacement of the hard drive was a fraction of the cost of a new RNS510 dab. We were surprised to find out that we had an SSD even though the date of Starlight was December 2014. Apparently the SSD's start to isolate bad patches of disc as soon as they are used. With time this builds up until there is not enough memory left to store the maps (which is why ours asked for the Navigation disc). Maybe it slows down performance too as it seems noticeably faster with the new hard drive. We have not had an SSD fitted but a normal hard drive which in this case are more robust as they are specially designed for automotive use. We also had a firmware update and V15 VW maps loaded. This was for less than 20% of a new RNS510 DAB.
So, all's well that ends well!
Thanks to all that made suggestions (Welshgas, et al) and helped us out getting to this point relatively quickly and cost effectively.