Pic 16f628a running at lower than 4.5V

[MegaADY]

Hello all. I have a project involving Pic16f628A. The power supply must be 3.5V. I looked in the datasheet and for that voltage I have to use a 10-14 MHz resonator. I am using 12MHz. The problem is that the pic won't start unless the power reaches 4.5V. Can anyone help me ? Thank you.

[MegaADY]

The BrownOutReset bit was activated, and the minimum voltage that triggers BOR is 4.4V. I disabled BOR and now everything is ok.