My Prusa I3 has stopped working after I built it

Hi everyone,

I built my prusa and used the LCD to check the movement of the motors and all was fine, I watched some videos on how to get everything up and running, they all said to download marling and arduino IDE to change all the settings i then followed on to update my firmware to the latest version for my MEGA2560 and after that things went bad. The words on my lcd were replaced by squares and then the lcd stopped displaying anything apart from rectangles, I changed all my setting back to what they were before and then it wouldn't allow me to upload it to the board. I then used pronterface to check everything was ok and then nothing was happening here is what comes up. I have tried everything to get it back but nothing is working and would really appreciate help.

Connecting...
start
Printer is now online.
echo: External Reset
Marlin1.0.0
echo: Last Updated: Feb 20 201620/02/2016 105611:38:18 | Author: (James Meredith)
Compiled: Feb 20 2016
echo: Free Memory: 3981 PlannerBufferBytes: 1232
echo:Hardcoded Default Settings Loaded
echoteps per unit:
echo: M92 X80.00 Y80.00 Z4100.00 E650.00
echo:Maximum feedrates (mm/s):
echo: M203 X120.00 Y120.00 Z2.50 E50.00
echo:Maximum Acceleration (mm/s2):
echo: M201 X120 Y120 Z5 E800
echo:Acceleration: S=acceleration, T=retract acceleration
echo: M204 S50.00 T50.00
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 X20.00 Z1.00 E20.00
echo:Home offset (mm):
echo: M206 X0.00 Y0.00 Z0.00
echoID settings:
echo: M301 P23.05 I2.00 D66.47
echoD init fail
Error:Temperature heated bed switched off. MAXTEMP triggered !!
Errorrinter stopped due to errors. Fix the error and use M999 to restart. (Temperature is reset. Set it after restarting)

I am very grateful for the help in advance.

plus i also have a buzzer that is constantly beeping

"Error:Temperature heated bed switched off. MAXTEMP triggered !!
Error: printer stopped due to errors. Fix the error and use M999 to restart. (Temperature is reset. Set it after restarting)"

means your hot end thermistor is probably shorted,
Take the hot end thermistor plug off the board, read the resistance threw the plugs, wires and thermistor, should be about 100K at 25c

I have done what you said and as you said it is broken so I will replace it thank you for the help