Thank you Melanie,

Actually, it still doesn't work.

Each time I press the button, the Led lights up and as soon as I release the button, the Led switches off. At least, it doesn't blink anymore while the button is pressed.

It just doesn't want to toggle!

To make sure my button is correctly connected, is this schematic okay?
> Vdd-R10k-PORTB.3 and the button (normally open) is derived from PORTB.3 to Vss.

Since I can't make it work with this simple program, my last guess would be that my PIC is defect. I tried with other ports but there is no change. I shall receive another PIC tomorrow.

By the way, is there any utility tool to check the PIC's health?