Dear Mann Manohar
Finally the Nvidia GeForce GT 420M GPU showed up by following Step2 otherwise since a long time there was no tracing of the GPU. Now at least it is confirmed that this thing is inside dead or alive and somehow disabled itself.
This is a Dell laptop XPS L501X model and my GPU was running well since last 5 years. One fine day I realized that my GPU is not working when I tried to lunch a Game. No idea how it got disabled and I'm the only person using this laptop.
Could you please guide me step by step how to enable it!! or what other methods to apply.