Dropdown menu problem

Hello everyone, I am having trouble with a site https://www.ltesdrinkwater.com . Dropdown menu doesn’t work and I guess it’s some changes I made in the header.php to optimize for speed with Performance Optimization: Order Styles and Javascript plugin . I am not sure it’s because of that though. I also installed w3 total cache recently but Don’t know how long the problem exists. I tried deactivating plugins , uninstall/install theme(schema theme) but no results. Any ideas?
Thanks