fastboot does not recognize my LAVA Iris Atom I've been doing quite the research on this error, but couldn't find a solution that could help me  with my device. 

Adb commands works fine, but not fastboot commands.

I have tried several sites for the fastboot drivers, in case that's the problem, but it didn't work. (I still have an exclamation mark on Android ADB Interface icon in device manager.)

My phone gets stuck at boot logo when I try flashing a custom ROM and I have to re-insert the battery to solve it. I rooted my phone using the KingRoot app. Does this have any relevance?
Right click on Not installed or Exclamation mark driver in device manager, click Properties, then click Details Tab. After that from Property Drop down list, click Hardware Id.
and copy first value from the box and google it by pasting in search.

i hope you'll get the right driver. 
Example:



Moreover, once you are sure that drivers are installed successfully, put your phone in Fast-boot mode to access otherwise fastboot command will not work.

in case you will stuck in process, let me know. 

Thank You