Hi!
I cannot see the rest of your code, but in the following line:
IE = 0x83; // setup interrupts
you are setting: EA, ET0 and EX0 bits. What about you timer 0? Are you using it? Maybe it overflows and timer 0 interrupt is executed?
And the second question is: why are you setting EX0 after "while(1)"? Controller is will never execute this line, isn't it?

Greetings,
Jacek