- how are you powering the ESP8266?
- use a voltmeter to confirm that GPIOs 0, 2, 15 and RST have been pulled up or down as required
- is your Prolific USB - serial adaptor 5v or 3.3v? If it's 5v, have you put a divider or other interface on the RX pin so you're not pushing a 5v signal into the ESP? 5v in can potentially kill the ESP.
- if you can get your hands on an oscilloscope, you can monitor the TX out from your ESP to see whether there's a burst of serial when it starts up. Also useful for checking all levels, looking for serial from the interface etc.
Not much more to suggest... I haven't yet had serial failure in 9 months and several ESP8266 modules.