Most likely explanation is that the printers internal CIS system is not pumping ink through to the printhead so the ink you have for those first 100 pages is what you get with your printhead as they all come with a small amount of ink pre-primed in them.
In terms of what could be causing it your options are:
1. Air leak in the CIS system
2. Failed pump mechanism in the printer (the white bit is not pushing into the cartridge bladder)
3. Failed pump mechanism in the cartridge (the black rubber bulk in the base of the printer needs to be pushed in to pump the ink into the system).
If you're using non-OEM/Original cartridges then that's probably a high likelihood for the failure... To be honest these printers are also known for the type of issue in 1. above as well..
Not much else I can suggest I'm afraid...
Printers: (Canon) MP500/830, MX700, iP4000/4200/4300/4500/5200, iX4000(A3) (Epson) C84/86, D88, CX6600, R285/800/1900 (HP) K550, K850, K5400, L7680