If that chip has failed (it's not clear why you think it has, and it's not a common point of failure) all you can do is replace the mainboard.
If you haven't tried a system reset (uplug system, hold power button for 30 sec, reconnect and power up again), that's something you should do.
So what should I do now? Should I replace the motherboard by sending it to Dell company? But my warranty period has gone. I purchased the PC in November 2011.
The boards cost about $130
It's your call as to whether to replace it yourself (it's not that difficult to do), or have a shop do the job - if you do the latter, look for a local shop that charges by the hour for labor rather than by the job. An hour's labor might be $75 or so depending on your location.
Then again, $200+ is over half the cost of a newer system. Weigh that in your decision.