<p>I've changed SD cards, printed from USB connection, upgraded/reloaded firmware and attempted using different software packages.  Nothing has worked yet.  When connected via USB, I get a &quot;disconnected&quot; error after a few minutes into the print.  Also, the LED lights now either don't work at all or will randomly go out after a few minutes - usually indicating that the print failure is imminent.  I've had the printer for about 4 years without issues.  I don't want to replace the motherboard only to find out it's the power source or vice versa.  Help?</p>

I recently had this problem and narrowed it down to the part cooling fan (on the side of the extruder head).  I diagnosed the problem by noticing that the printer would reboot shortly after the second layer started, only on PLA prints.  Of course, the part cooling fan is not usually started until after the first layer.  It was shorted and when the printer got to the second layer it would overload the power supply and cause a reboot.  Took a while to determine this, but it is worth looking at if somebody else is having this problem.
I would guess that any shorted fan, even the extruder fans, might cause a similar issue, however, I don't know this for sure.