Esp-Link troubleshooting

verify that you have sufficient power, borderline power can cause the esp module to seemingly function until it tries to transmit and the power rail collapses
if you just cannot flash your esp8266 module (some people call it the zombie mode) make sure you have gpio0 and gpio15 pulled to gnd with a 1K resistor, gpio2 tied to 3.3V with 1K resistor, and RX/TX connected without anything in series. If you need to level shift the signal going into the esp8266's RX use a 1K resistor. Use 115200 baud in the flasher. (For a permanent set-up I would use higher resistor values but when nothing seems to work these are the ones I try.)
if the flashing succeeded, check the "conn" LED to see which mode esp-link is in (see LED info above)
reset or power-cycle the esp-link to force it to become an access-point if it can't connect to your network within 15-20 seconds
if the LED says that esp-link is on your network but you can't get to it, make sure your laptop is on the same network (and no longer on the esp's network)
if you do not know the esp-link's IP address on your network, try esp-link.local, try to find the lease in your DHCP server; if all fails, you may have to turn off your access point (or walk far enough away) and reset/power-cycle esp-link, it will then fail to connect and start its own AP after 15-20 seconds

Assuming appropriate hardware attached to GPIO pins, the green "conn" LED will show the wifi status as follows:

Very short flash once a second: not connected to a network and running as AP+STA, i.e. trying to connect to the configured network
Very short flash once every two seconds: not connected to a network and running as AP-only
Even on/off at 1HZ: connected to the configured network but no IP address (waiting on DHCP)
Steady on with very short off every 3 seconds: connected to the configured network with an IP address (esp-link shuts down its AP after 60 seconds)

The yellow "ser" LED will blink briefly every time serial data is sent or received by the esp-link.