No response to m105 command

My MakerGear M2 has suddenly decided to stop responding to commands. It does the normal reset when you start the connection but then the firmware never seems to respond after sending back the SD card status is okay. Sending a M105 command generates no response and no more led flashes on the TX side. I see Rx led flash each time I send a command but no response after the initial reset. What could cause the Marlin firmware to stop responding at this point? Is there any way to get more debug info out of it?

Connecting...
start
Printer is now online.
echo: External Reset
Marlin 1.0.0
Using tool 0.
echo: Last Updated: Apr 26 2015 20:59:26 | Author: (none, default config)
Compiled: Apr 26 2015
echo: Free Memory: 4141 PlannerBufferBytes: 1232
echo:Hardcoded Default Settings Loaded
echo:Steps per unit:
echo: M92 X88.88 Y88.88 Z400.00 E471.50
echo:Maximum feedrates (mm/s):
echo: M203 X500.00 Y500.00 Z25.00 E25.00
echo:Maximum Acceleration (mm/s2):
echo: M201 X4000 Y4000 Z100 E10000
echo:Acceleration: S=acceleration, T=retract acceleration
echo: M204 S2000.00 T3000.00
echo:Advanced variables: S=Min feedrate (mm/s), T=Min travel feedrate (mm/s), B=minimum segment time (ms), X=maximum XY jerk (mm/s), Z=maximum Z jerk (mm/s), E=maximum E jerk (mm/s)
echo: M205 S0.00 T0.00 B20000 X8.00 Z0.40 E5.00
echo:Home offset (mm):
echo: M206 X0.00 Y0.00 Z0.00
echo:PID settings:
echo: M301 P25.89 I1.94 D86.53
echo:SD card ok
SENDING:M105
SENDING:M105
SENDING:M105