In my experience this problem is with hardware, not software. The first thing is to rule out a bent or damaged usb pin as catymag suggested. The 1xxx series also has an inherent problem with the usb socket, especially happens with 14xx, but not unknown on 13xx. Often the soldered connections to the PCB fail and need to be reflowed, a delicate task but not hard if you have the right equipment. Sometimes the problem is due to a component failure on the board, which is harder/impossible to fix. Generally, if both data and charging are compromised it can be fixed with reflowing the connections. If it's only one of those that's a problem and provided the usb socket itself is ok then it's possibly a PCB problem and reflowing may or may not help. As your unit will charge but cannot be seen by PC in either MSM or preboot mode the problem is probably hardware problem of some kind. However, if you haven't already done so you should clear NV. On map page, press speed field>press and hold centre of speedo for ~5-6 seconds to reach Diagnostics Page>Developer Info>Nonvol Available>Clear nonvol>Yes. You will lose favourites, but if that's a big problem for you you can restore from the backup. It's worth a try. After that, do a firmware upgrade to V6.20 from microSD:/Garmin/gupdate.gcd even if the usb still won't work. Then clear nonvol again.