Not sure if it's 100% across all windows installs, but my client Gmod installed to D:\Program Files\Steam\steamapps\common\GarrysMod
(Your's is missing "common") I've also not seen an apostrophe used in the folder name, but again, that might not be 100% common for Windows.
Does ULib give a startup message in console?
Do you have addons/ULib/addon.txt and addons/ULX/addon.txt both?