@CyanClaw33 Ideally, you install previousbuild Besiege, then download the installer, telling Windows/Your AV/Chrome/whatever that you actually do want to run it, and then it should work.
If it doesn't, you can try the manual installation again, but make sure you *first* switch to previousbuild and then install the mod loader. It wasn't quite clear from your post if you might've done it the other way around.
If that still doesn't work, upload the output_log.txt file from the Besiege_Data/ directory after you tried to start the game and it crashed/didn't work.