Navbar dropdown menus stopped working in chrome & IE

[JamesAB]

I have a bizarre problem that is probably template related.

The dropdown menus in the navbar stopped working in chrome & IE, however they still work in Firefox.

If I switch from my styles to the "Default Style" they seem to work again.

How can I troubleshoot this?
What files or vBulletin components are needed to make the navbar dropdown menus function properly?

I tried simply copying the navbar tempate from the "Default Style" to my own style, but that didn't fix the problem.

Thanks for your help.