Before you go further, most important question: Does the computer still detect your USB? If so, you're still not totally screwed.
And when you say it says Unknown, are you talking about LGNPST or your actual phone. I need to know if you see zeroes on the phone itself. If LGNPST is saying Unknown on it's display, your phone isn't being properly detected by the software. Attempting to do anything while it says Unknown will only brick your phone if it connects to it at all.
1) Download and install LG Updater from the LG website. Choose Recovery Phone from the Customer Support drop down and enter the required info. If you're told "Your phone is already up to date", move on to option 2 or 3.
2) Try the steps posted here:
http://androidforums.com/optimus-m-all-things-root/342765-how-do-i-un-root.html#post2738263 to at least see if you can get your phone back in working order. Make sure drivers are installed properly. If you have Vista/Win7, you may have to play around with UAC and run in XP mode to get things working properly.
(If LGNPST still says unknown after properly installing all the mentioned software, don't even attempt anything further. See option 3)
3) If you still can't get LGNPST to recognize your phone and LG Updater wouldn't do the update, send a PM to
Joneidy or
Blaxican25. They've been great at 1-1 helping of people in your situation.