When I unplug cable of AMT and then replug it, then it does't reponds to ping until I PowerOn the machine, Once power Up now it responds to ping all the time whether u do a reset, power on, power off, why is it so ?
I agree with Gael's suggestion to check that the ME state is set to always ON in the ME configuration. Apart from that, before you unplug the network cable, were you able to ping AMT regardless of the host power state?
Remember that once you unplug the network cable and plug it back in, AMT would require some time to recover from the event and once the network stack is back in operational state, you will be able to ping again. Are you using static IP or DHCP configuration?
One other test I would do is after you plug the cable back in, give it some time and try the ping. If the ping does not work, try accessing the web UI to test the connectivity. Hope this helps.
Sorry for not mentioning the cable type, I was actually talking about power cable not network cable. When I initially connect power cable to machine (before this machine will be totally in off state including AMT hardware) it does't respond to pings and also not discoverable by Commander, until i press the power button on CPU.