Re Install android OS in Mobile Phone I am using LG optimus E 400.

Recently, I have rooted my Android phone. After rooting, it's not booting up now; just displaying white screen. 

I have tried go to the boot loader by pressing (Hold POWER + Vol Down) but it's not working in my phone. 

After some searching in Google, I found that the solution is re-installing the Android OS. How do I do that? Is any other recovery option? 

Thanks.
Solution as per link provided by OP:

Vijesh finally was able to solve his issue using the All-In-One Toolkit, following the instructions from this XDA thread. This toolkit requires Windows. Not explicitly mentioned in the XDA thread, but most likely this means you've also to install the appropriate device drivers for your smartphone. But it looks like the toolkit offers to do that for you as well, see the item I - Install APX drivers in below screenshot:


The All-In-One Toolkit (Source: XDA; click image for larger variant)

The tool seems to be pretty self-explaining. For the installation, you simply run the self-extractor, which prompts you for a target directory. Then you start the tool, and select the wanted item (here probably 6 - LG Update Tool). Again, everything runs almost automatically -- simply follow the instructions given. The .kdz file should be flashed then to the device, and you'll end up with the fresh ROM installed.