Every imaging unit has a life. There is a chip which gets signal from imaging unit about when to stop printing. That is the reason when it stops the page before that prints just fine. And we thing that it can print lot more pages. But this is not true. You should buy a new one.
Having said that still there is a way to rest the ram on the chip so that it ignores the signal from imaging unit. You can try to reset that and see if it prints more pages. Here is the instructions to reset.
1 Turn the printer off.
2 Press and hold the GO button.
3 Turn the printer
on and continue to hold the GO button.
4 After the Go, Ready, and Attention
LEDs turn on, continue holding for at least 20 seconds.
During this process,
the Attention, Ready, and Go LEDs will each turn off.
5 Release the GO
button.
6 The device LEDs will begin cycling from front to back. The
NVRAM-init process runs until the
printer is in the Ready state.
7. Press the red cancel button.
For more info goto
here.