Hi Prashant,
Suggestion:
1. I feel your Port setting have some problem, you pls check once.
2. You may also try to flush the port (when you go for next cycle of
write/read).
3.You may go to this link for serial Port Programming
http://www.easysw.com/~mike/serial/serial.html

If you still feel problem write to me again, I will send you the port
and other related settings.

bye
T.K.Saini