Kindle can't start after entering DIAG mode

[geekmaster]

Originally Posted by HarryT

You can't. If your computer doesn't have a serial port (and virtually none do these days), you'll need to get a USB serial port adapter.

And even if your computer DOES have a serial port, you still need a TTL serial port adapter BECAUSE computer serial ports are RS-232, which inverts the signals and uses up to +/-12V signal levels. Such an adapter will probably have some variant of the MAX232 chip in it to convert those voltages to a TTL level (5V or 3.3V is common), but even that needs to be converted down to the 1.8V logic levels used by the kindles.

So even if your computer has serial, it is a lot easier (and cheaper) to just use a USB TTL serial adapter cable, as is often discussed in this forum.