There is a small grain of rice looking fuse on the control board that may need replaced. You also may need a new LCD board but they are only $40 or so. The fuses are about $0.50. Lulzbot or itworks3d.com sell them.
Adjust your usb port power under the power item on control panel settings on your computer to “Never sleep” it may also be some program freazing the usb ports. Opening winamp for example will do that.
The z axis issue isn’t normal. You either have debris in the leadscrew nut, a loose coupler, a broken coupler, a motor that’s going bad, or a control board issue. It’s most likely debris in the nut. The fix is a good cleaning and possibly a replacement nut. Doing so requires taking the machine apart but you are out of warranty anyways. It is just as much a pain in the ass as it sounds.
The plastic leadscrew nut itself. The thing that goes up and down on the leadscrew, that bolts onto the z carriage. It’s kind of shaped like a T if you look at it from the side, and is held on by m5 bolts.