Well, making the assumption that the serial port itself is fine, then it looks like the CPU is unable to load the bootloader from flash. As I see it, there are three major reasons why this wouldn't happen;

1) CPU not working.
2) Flash not working,
3) Something else that shares the data/address busses not working.

The first thing that you should probably do is verify Vdd on the CPU and flash. Given that the fuses are fine I'd expect this to be a formality, but do it anyway.

Beyond that, you'd really need a scope to test further. There isn't much on the CPU address/data lines - Flash, RAM and line transceiver. Everything else lives behind the line transceiver (Which I believe should prevent a problem with downstream components causing this particular symptom). It would be useful to check the CPU clock circuitry too.

One other test that you can try is to leave it powered up for a couple of minutes and see if any of the chips get hot. This will often indicate a bad chip (_but not necessarily the root cause_,)

Remember to take anti-static precautions when touching anything internally.