user6408: I have an Arduino Pro Micro clone that seems to be in some sort of reset loop. The RX LED is flickering very fast and very dim. The power LED also seems to flicker at the same frequency but has normal brightness.
The Arduino is not recognized by the PC at all anymore. It was working fine before. It doesn't matter if I try to go into the bootloader, by pressing reset twice, or not. Nothing happens. It feels like it is constantly resetting. The flickering stops if the reset pin stays connected to GND.
Another clone from the same shipment is still working fine. Both running the blink sketch. Just this one started to malfunction all of the sudden - after probing the pin I set in the blink sketch with my multimeter to see if the flashing was a success.

user10003: I bricked my Pro-Micro within ten minutes of ripping it out the packet. I didn't realise that (a) it's not so brilliant on USB 3.0 - or in my case, unuseable, and (b) it's not actually an Arduino board - the Pro-Micro is a SparkFun product, and any clones thereof are from SparkFun's schematics.
The latter was only a problem to begin with, while I was scrabbling around on the Arduino website in vain trying to find answers. Once I realised to visit SF's website everything calmed down. Read this section on bricked/unrecognised pro-micros, and then have a look at the rest of the page as further reading.

user6740: Try this: unplug the Arduino, hold down the reset button, and then plug it in to power. Hold down the reset button a few seconds after you power it on. If this works, you should get the "blink" sketch, and be able to reprogram it. 
Alternatively, if you have an ICSP programmer (I use the FreeTronics USBASP), plug this in (you will need to wire up the appropriate 6 pins), and then use the Arduino IDE to burn the bootloader - select the board, serial port, and programmer,then select "burn bootloader" - all from the "Tools" pull-down menu. 

user30630: Try this:

Connect a push button switch to ground and reset (RST) pin;
Click upload then push the button twice (fast) = it doesn't matter if your computer does not recognize the pro micro;
Repeat this if it failed (repeat until you are successful).

After this the Pro Micro port will comeback to life.
I tested it. The reason I think that you bricked it, is because you uploaded using the wrong board setting - commonly the 3.3 V and 5 V (or vice versa)

user6936: This is a very common problem. See my answer to Arduino Micro just blinks, won't connect to PC. 
As Asenkhan says in his answer, it is often caused by attempting to upload to a Pro Micro using the wrong board setting 3.3 V en lieu of 5V, or vice versa.

I have written two lengthy blogs about the whole experience:

The case of the broken Pro Micro
The case of the broken Pro Micro (reprise)


user11460: If your pro micro does not have a reset button, wire one between reset and ground. 
Press reset twice, quickly, and immediately hit upload on the IDE.
Secondly, make sure you've downloaded and installed the Sparkfun board files for the pro micro. 

6408: <p>I have an Arduino Pro Micro clone that seems to be in some sort of reset loop. The RX LED is flickering very fast and very dim. The power LED also seems to flicker at the same frequency but has normal brightness.</p>

<p>The Arduino is not recognized by the PC at all anymore. It was working fine before. It doesn't matter if I try to go into the bootloader, by pressing reset twice, or not. Nothing happens. It feels like it is constantly resetting. The flickering stops if the reset pin stays connected to GND.</p>

<p>Another clone from the same shipment is still working fine. Both running the blink sketch. Just this one started to malfunction all of the sudden - after probing the pin I set in the blink sketch with my multimeter to see if the flashing was a success.</p>
 10003: <p>I bricked my Pro-Micro within ten minutes of ripping it out the packet. I didn't realise that (a) it's not so brilliant on USB 3.0 - or in my case, unuseable, and (b) it's not actually an Arduino board - the Pro-Micro is a <strong>SparkFun</strong> product, and any clones thereof are from SparkFun's schematics.</p>

<p>The latter was only a problem to begin with, while I was scrabbling around on the Arduino website in vain trying to find answers. Once I realised to visit SF's website everything calmed down. Read <a href="https://learn.sparkfun.com/tutorials/pro-micro--fio-v3-hookup-guide#troubleshooting-and-faq" rel="nofollow">this section on bricked/unrecognised pro-micros</a>, and then have a look at the rest of the page as further reading.</p>
 6740: <p>Try this: unplug the Arduino, hold down the reset button, and then plug it in to power. Hold down the reset button a few seconds after you power it on. If this works, you should get the "blink" sketch, and be able to reprogram it. </p>

<p>Alternatively, if you have an ICSP programmer (I use the FreeTronics USBASP), plug this in (you will need to wire up the appropriate 6 pins), and then use the Arduino IDE to burn the bootloader - select the board, serial port, and programmer,then select "burn bootloader" - all from the "Tools" pull-down menu. </p>
 30630: <p>Try this:</p>

<ol>
<li><p>Connect a push button switch to ground and reset (RST) pin;</p></li>
<li><p>Click upload then push the button twice (fast) = it doesn't matter if your computer does not recognize the pro micro;</p></li>
<li><p>Repeat this if it failed (repeat until you are successful).</p></li>
</ol>

<p>After this the Pro Micro port will comeback to life.</p>

<p>I tested it. The reason I think that you bricked it, is because you uploaded using the wrong board setting - commonly the 3.3 V and 5 V (or vice versa)</p>
 6936: <p>This is a very common problem. See <a href="https://arduino.stackexchange.com/questions/2987/arduino-micro-just-blinks-wont-connect-to-pc/30604#30604">my answer</a> to <a href="https://arduino.stackexchange.com/questions/2987/arduino-micro-just-blinks-wont-connect-to-pc">Arduino Micro just blinks, won&#39;t connect to PC</a>. </p>

<p>As Asenkhan says in <a href="https://arduino.stackexchange.com/questions/6702/arduino-pro-micro-clone-not-recognized-flickering-rx-led#answer-34241">his answer</a>, it is often caused by attempting to upload to a Pro Micro using the wrong board setting 3.3 V en lieu of 5V, or vice versa.</p>

<hr>

<p>I have written two lengthy blogs about the whole experience:</p>

<ul>
<li><a href="https://gr33nonline.wordpress.com/2015/08/05/the-case-of-the-broken-micro/" rel="nofollow noreferrer">The case of the broken Pro Micro</a></li>
<li><a href="https://gr33nonline.wordpress.com/2016/10/19/the-case-of-the-broken-pro-micro-reprise/" rel="nofollow noreferrer">The case of the broken Pro Micro (reprise)</a></li>
</ul>
 11460: <p>If your pro micro does not have a reset button, wire one between reset and ground. </p>

<p>Press reset twice, quickly, and immediately hit upload on the IDE.</p>

<p>Secondly, make sure you've downloaded and installed the Sparkfun board files for the pro micro. </p>
