I don't think it's Lightroom. I think it's a Windows setting, maybe in the "File Handling Preferences" or "Default Programs" where you can select which program starts when a file with a certain extension is opened. For example, you could tell Windows you want to open JPG's with the Windows Picture and FAx Viewer, then anytime you double-click a JPG, it starts that program. But, maybe is Lightroom. Did you look through all the options in Edit/Preferences. I don't use LR, so not sure about that menu.
If there is a setting in there that can be tweaked it might help you. I know when I installed a LR trial, even though I had always used ZoomBrowser to import files from CF cards, whenever I inserted a CF card in the reader, Lightroom would start.
I know where you can find your answer - NAPP - National Association of Photoshop Professionals. Anyone can join, like me. It cost's $99 a year, but you get the Photoshop User magazine, and TONS of helpful tutorials, video and written, and discounts on ADobe software and other stuff, and their Help staff is awesome, in my experience.
I had an issue I couldn't figure out when I had 400 files I wanted to resize and make into a collage-type thing. I filled out the Help form, got an answer about 8 hours later, and it worked perfectly.
I just logged in to my NAPP gallery, and there was a "Refer A Friend" blurb. Not much in it for me ( I would have to refer about 15 people to get much -= like my membership extended). However, if you do decide to join and use this link
, it says you get a free copy of a DVD that's s omething like "Photoshop - top Tips & Tricks" or something.
NAPP is the org that Scott Kelby started, I think.