mobile

So I am new to this forum and need help. I was trying to downgrade my LG G3 on Sprint from Lollipop (5.0.1) to stock firmware, however when trying to use the LG Flash Tool, it kept coming up with Fail USB open port fail. I figured that switching the ports might help, but it kept coming up with the same error message.

I am considering installing Cyanogenmod, but that is like the last ditch effort for me. I do not want to void the warranty yet (ive only had the phone for a few months now). I should have just hit factory default, but wasn't sure how far back it would've taken my phone. The latest version has been pissing me off when it came to the sporatic battery life drains. I now have learned my lesson on that, but would appreciate any help when it comes to getting my phone hopefully back to stock settings. I am gonna take my laptop to a local coffee shop in hopes that I can get some success on it. All the work has been on my desktop. I think the software hates my mobo or something.