If you have setup a plugin incorrectly or setup a bad plugin your Xbox 360 will either boot to a black screen, boot to the Xbox 360 boot animation and freeze or boot, crash and then restart. A an example of a bad plugin is a poorly coded mod menu or stealth server. Here are instructions on how to fix this.
First trying holding down RB on your controller as the console boots. If this works once the console boots go into Dashlaunch and remove the plugins you have installed. Remember to save before you exit Dashlaunch. This only works if you have a corded controller or a wireless controller that syncs before the plugin is loaded.
If the above does not work you will need to download this file LAUNCH.INI and place in on the root of a USB drive that is formatted to FAT32. (make sure it isn't in any folder)
Plug the USB drive into your Xbox 360 and power it on. This file will force you Xbox 360 to boot with no plugins loaded.
Once the console boots go into Dashlaunch.
Press RB on your controller and go down to FLASH (or where your original launch.ini is saved) and press A to load your original Launch.ini file
Press LB on your controller and go down to plugins and press Y on every plugin that has a path in it.
Press RB again and go down to FLASH (or wherever you want to save your launch.ini) and press X to save your new launch.ini.
Press B to exit Dashlaunch
Your console should now boot again correctly (remember to unplug the USB drive that has the blank launch.ini file on it otherwise the Xbox 360 will default to that one again)
We are unable to fix/repair a bad plugin. If a certain plugin is not working correctly there is nothing you can do other than go back to the person who has made the plugin and see if they can help you.
*having multiple launch.ini files is a bad thing so ensure you only ever have one on your console and delete any unused ones. (i.e. do not have one on FLASH and one on your HDD1 etc)