Fix the menu of a site - Hiring now

The problem is, the menu seems to work only if you allow the page to completely load up. In some cases, the menu won't work at all, in some cases, it will work. I want the on and off of the menu to stop. I want the menu to work permanently. I also want the menu to work even when the page is loading. There are some bugs on the site which I want fixed. I want the site to load faster. Is this something you can do? Thank you