There's a whole lot there that is not explained, and appears to have nothing to do with serial comms.

You need to go back to basics, and start with a simple "Hello, world" program that does nothing else but send "Hello, world" to the serial port using your interrupt-driven stuff.

Once you've got that working, move on to receiving serial data.

Once you've got both sending and receiving of serial data working, then - and only then - move on to integrating it with other stuff.

NB: Why re-invent the wheel?

There is perfectly usable, ready-made code on the Keil site for you to use:
http://www.keil.com/download/docs/200.asp
http://www.keil.com/download/docs/71.asp

(you haven't stated what tools you're using - I'm guessing Keil, but it shouldn't be hard to adapt to other tools...)

See also: http://www.keil.com/forum/docs/thread11543.asp