people i have a friend who is in trouble..actually he could not access net,so i am writing on his behalf..
while testing his setup,,a problem occurred and it stopped working.now when he switched on his tx and connected battery,his system didn't responded..according to him his setup was working fine and suddenly stopped.also no foul smell from esc and motor..
pl help.

What is not working? radio or esc+motor.

Fastest solution is to take it to someone experienced locally.  Troubleshooting these things online would be difficult.  Even someone guiding over the phone, with step by step checking of the various components involved may work.

Typically "it stopped working all of a sudden" is not what really must have happened.  Any investigation is really dependent on someone explaining IN DETAIL what those 3 words really mean ("a problem occured") !

Mase..make sure the batteries used in the transmitter is good. make sure the power indicator on the transmitter showing the power level in to feasible range. then check the battery that you connected to the ESC. make sure the output voltage reaching at the tip of the terminals of the battery pack. make sure there wasn't any short circuits between battery terminals. if so, the fusible link may opened, inside the battery pack if have. if found ok, make sure a 4.9 or 5 volt is reaching at the terminal of the ESC line to the receiver, means three coded wire, and between red and black, with multi meter. if not, check the ESC, for input impedance and out put impedance according to manufacturer's specifications. if found ok..make sure all connected polarity is in needed direction.means wire of the servos and ESC line. if all found ok, think about your radio as, is it a conventional MHz based radio, or a 2.4 GHz SST. if it is a 2.4 GHz SST, or DHM, you must re BIND it once (PAIRING), and try again. if still persists, connect a 4.8 volt source to the receiver, from an other source and try it. if still persists, you must go for a through check up, through the internal circuits.

he is using flightmax 1000 mah 3cell lipo with mystery 20 amp esc..
according to him it happened while his motor was working and suddenly it stopped..now there is no beep sound coming from esc neither light flashing on receiver...what say people??

Mase..try to connect an other battery pack, to the receiver. and check the D connector of the battery pack and ESC. make sure the supply is reaching at the tip of the battery pack terminals. try with an other battery pack.if it runs your ESC need a reprogramming. some ESC and receiver get malfunctioned due to some SAW interference. and BIND the system, if its a 2.4 GHz system.and try with an ordinary 4.8 volts battery pack, only receiver with servos. if so, you can finalize the problem is at battery pack side..

he said he had bought this battery few days back.earlier he was 1200ma lipo...he connected that new battery yesterday  only and this problem occurred...but he says the battery is genuine and there is no problem with it..

Mase...listen me once..the battery pack may be a new one. but by eyesight we cant predict the nature of the connector. thats why i told you to check the D connector. and most of the ESC s are designed as programmable, means you can set it's threshold, voltage ratings, battery counting, battery types, hi and low end settings, normal, soft, super soft, start ups, and many..when we connect a fresh battery pack, to an ESC it will count the numbers of connected batteries, by the total voltage, or by the threshold, and if any excess happen, from the programmed level, it will not respond.so, try to connect the previous battery once again..and make sure the 4.9 volts BEC ( Battery Eliminator Circuit Voltage), is reaching at the wire tips of the three coded ESC line to receiver. but prior that make sure the battery voltage is reaching just behind the male D connector with multi meter.

try to start by removing the connections of the BLDC, once, because some short circuits in BLDC windings prevent the ESC to start up..

Try and meetup with the setup and let's see what is wrong

try with ARCH mode and listen for a any feedback..

sir what do you mean by ARCH mode?

Mase..ARCH mode is an advanced mode of testing of the CPU, or EPROM based ESC s. before going in to that level,you must try with an other battery pack,and by connectors. once again, make sure the mentioned voltage is reaching at the tip of the battery pack. and by giving a car head light bulb, you can check its capability, in load.but make sure to avoid short circuit. means shorting the power terminals to gether. and after that, read the voltage just behind the FEMALE D CONNECTOR, of the ESC. if the right voltage is there there must be some problem with ESC. some of the defect in PCB of the ESC can rectify, but a defect related to MCP is almost unserviceable...