Debugging an FPGA board

I recently made a PCB for a Spartan 3 XC3S00 FPGA. I'm now trying to program it through the JTAG port, but chipscope does not seem to recognize the FPGA, so I'm worried that I routed something incorrectly. After chipscope says "cable connection established", it then says "ERROR: Failed detecting JTAG device chain." This is my first time making a PCB for an FPGA, so where should I begin checking to see what's wrong? It seems like all of the JTAG signals are correctly routed to the FPGA.  I tied HSWAP_EN low, so the configuration pins on the FPGA that I did not ground should be high, correctly configuring the FPGA for JTAG mode. Any advice would be greatly appreciated. Thank you.