Please help me out, i have connected my ipad to Bluetooth keyboard and since then my virtual keypad has vanished.

Please tell me how to retrieve back my virtual keypad on my ipad2

I did the same thing and had to turn Bluetooth off to get the keyboard back. I might not have turned off my keyboard so it may have still been connected.
Try turning the keyboard off and if that doesn't work turn bluetooth off.

I had same problem with icade connected, keyboard vanished, turned of Bluetooth and prob solved

Well, when the Apple wireless BT keyboard is on and paired w/ the iPad, the virtual keyboard is disabled by default - to reactivate the virtual keyboard, press the eject button (upper right corner) on the physical KB (this will toggle the virtual one on & off) - more information HERE, if interested.