Hi,

Internal pull ups are weak as stated and Steve is again damn right. Optocontrollers do help but then you need an additional power line light the LEDs. PCB layout is equally important. If you post your whole code then we can find out if it is an interrupt issue. Normally a PIC would reset if it freezes, (WDT) so an improper code may put your PIC in endless loop especially interrupts. If you do not have an ICD then it is possible to dump some values of the SFRs related to PIC power, stack etc,. This would ease diagonisis what went wrong and where.