Hello,
While developing I have already bricked 3 Arduino Pro Micros.
These devices were bought from china via ebay.
It all happened by uploading while having a serial connection. So, the result was that the programming stopped in the middle.
Now, they won't flash the green leds at all. The only led being on is the red one meaning power.
How could I bring these devices back to life?
I have an arduino mega and an avr isp mk2.
Can you make a photo of them ? Do they have the ATmega328p microcontroller ?
I'm not sure they are the Sparkfun Pro Micro boards.
Can you also make a photo of the wiring ? I hope you didn't connect the RS-232 signals directly to an Arduino board. That would destroy them.
Peter_n:
Can you make a photo of them ? Do they have the ATmega328p microcontroller ?
I'm not sure they are the Sparkfun Pro Micro boards.
They are really the same. Even the exact same bootloader.
They are indeed like the Sparkfun Pro Micro, like a clone from a clone.
I hope your programmer didn't accidently set the HV programming.
When they got bricked, was nothing connected ? only a usb cable ?
You mentioned a serial connection, that got my attention. What kind of serial connection ?
There indeed was a radio transmitter (433Mhz) connected to pins 2, 3 and ground, and a serial via usb.
These arduinos were communicating with my pc sending data back and forth in addition to programming via usb/serial.
Only one arduino was connected at a time.
The transmitter is okay, I assume you used the Arduino 5V pin to power it.
Can you explain once more... or make a drawing or photo of it 
You have a usb cable connected to the usb connected.
Plus you have another serial connection to the computer ? how ? also with a usb-to-serial-ttl converter ? Not directly to a real RS-232 port I hope.
There's only one physical connection: the usb cable.
While communicating via usb (serial) between arduino and pc, and then uploading a sketch, the upload process will stop in the middle. After this there will be error messages of a broken pipe. After unplugging and replugging arduino to usb it won't be recognized anymore.
Arduino <-> usb <-> PC
Edit: It's easily repeatable. I could make a video about it but I'm getting short of arduinos 
Perhaps you have a bad bootloader. Something must be very wrong.
You can try two things:
1 ) Use Arduino 1.5.7 BETA, and use the programmer to write the new bootloader. Select board Micro and write the bootloader with the Arduino IDE. Also the fuses will be set with the Arduino IDE.
2 ) Use the bootloader "Caterina-promicro16.hex" from the Sparkfun page : https://www.sparkfun.com/products/12640
They are dated 25 aug 2014, so they are very recent.
If that all doesn't work, throw them out of the window 
and forget about them. Use a normal board, like the official Arduino Micro : http://arduino.cc/en/Main/arduinoBoardMicro
Sometimes you have to fall back to a known situation that does work.
Lol, I just fixed all of them.
Connected atmel's avr isp mk2 to arduino pro micros and burned a bootloader using arduino ide 1.0.5.
Cool 8)