EP2C5T144 mini devboard JTAG issue

I recently owned the http://www.leonheller.com/fpga/ep2c5t144mini.pdf board, also did some flashes via JTAG. But today, I don't know why, I can't flash via JTAG anymore. I just get the error: Unable to read device chain. (JTAG chain broken)

Why is this error happening? How to fix it?