When you say mod folder, do you mean the user folder? Make sure you check the openxcom section of the user folder. But if all mods are switched off then it should give you the vanilla experience.
If you can't figure out how to make it work, you could check your base ruleset for the laser weapons research projects and see what's going on. Make sure all of the topics are in place and that there aren't any delete: lines in which would remove them. Another thing to do is install a mod that rewrites the laser weapons tree from scratch, such as pretty much any total conversion mod, probably Final Mod Pack or Area 51, I know that XCOM Files and Robin's Apocalypse mod do this, as does my own megamod if you want something closer to vanilla feel.
The solution is probably obvious and staring you in the face, but based on what you've said, I'm at a loss as to what could be causing it. I feel like a fresh install should definitely fix it. Just double and triple-check that you have no mods running. They can be installed, they just need to be set to off.