"I have connected this keyboard with PC, I swipe the card and get corrected digits using notepad and wordpad.."

Did you need to install a special driver on the PC for this?
If so, the keyboard may not be using "normal" scan-codes for the card swipe; it may be using some proprietary, non-standard mode.

Remember that the PC/keyboard interface is bidirectional, and the PC can command the keyboard into various operating modes - maybe you need to handle some special command modes?

Do you have some sort of analyser that can monitor what actually happens on the PC/keyboard interface when you swipe a card?
eg, a logic analyser, or a deep-memory storage scope?
(there was a thread here a while back about a freebie simple logic analyser using the PC parallel port - try a 'Search')