Use Windows Explorer (with show all hidden files & folder option ticked) to make a backup. Just copy everything from your ?:\ drive to a safe place.
I'm trying to get your Go 520 to a fully working condition on the internal drive with the latest UK & ROI map....primarily as a test of the device.
Once that is confirmed, you can copy the whole setup over to the SD card but this time with the latest USA map. The idea being that you'll have a fully tested & known working device for use at home on the internal....and then when in the USA, you can just put the SD card in and hey presto, known working system but now also with a USA map.
So I'll say it again, follow my instructions in post #11 as we need a tested system that we can work from.
In the mean time, download the following map from [Please Register or Login to download file]
United_States 990_8362 = 1.17GB