Hello parag_250, and welcome to Android Forums.
Sorry to see you're having reboot issues with your device after setting up wifi. It may be a good idea to first disable wifi just to see if the reboots are really related to the network in some way.
If the rebooting stops once off wifi, it may be a good idea to clear all cache and data from your networking apps and widgets in the application manager, then reboot and set up wifi again to see it the problem went away.
Is it a home network or other network you have control over? If so, maybe a channel change on the router will help. It may also help to just try restarting the router.
I've moved your question to the LG Optimus 2x forum for you. Others with that particular device may be able to offer more assistance.