Simple PORTA Control via PIC
I suspect that you have not set the ANSELA register correctly.

The port defaults its analog-capable pins to analog mode, which means that when you read them through the PORTA register they will read as 0's, irrespective of what the voltage level actually is on the pin.
But, you can still set output values, which is why you can toggle the pin.

So, set your ANSELA bit 0 to 0 to set it to digital mode (and for any other pin you plan to use as an input) and you'll be able to read inputs correctly.