TMR0 stops working

[shahidali55]

I have made a Digital led clock using the following hardware :-
PIC16F84A (used it as i have many lying around)...
4X 9 volt led displays

The time keeping is managed by TMR0 and Instant Interrupts.
The problem is that the TMR0 suddenly (and randomly) stops incrementing while the chip is on. This may happen in a few hours or in a few days or even after a month.
The oscillator still clocks at 4 Mhz , the chip still keeps the display running (multiplexing), the time set buttons still work.

I have been trying to fix this problem from the past 1 and a half year, but nothing seems to work.
I tried using a 16F628A, still no luck.
Now i really need some help.
I have attached the complete source code and schematic.
Can someone please help me ? ? ?

PSU.JPG = power supply with battery backup
clock.gif = base circuit
12Volt Driver.bmp = modification for large led displays
clock.pbp.txt = main source code
DT_INTS-14.pbp.txt = Instant Interrupts subsystem