Does the phone start itself (e.g. when you put the battery back in)? If it does, there may be a hardware problems with one of the modules.
Did you install openGAPPs? If you did, you’ll need to flash those again to get out of the boot loop (see this useful guide if you need hints on how)
What do you mean when you say sideloading hasn’t worked - does the update file not install, or does it install, but not solve the boot loop?