There has been a lot of discussion on PC keyboards here before - do a 'Search' for "PS2", "PS/2", "keyboard" etc

"iam using delay in the program for the key rebounce time"

Do you mean debounce?

A PC keyboard is already debounced!
Your problems are probably all due to your delay - take it out; you don't need it!

Don't forget that the PC keyboard sends two scan codes for each key: one for key down and another for key up