On my laptop my game loads fine but when I click enter world it stays at 0% loading screen and lags out. I have tried all versions - retail, classic TBC and classic SoM/Era and they all do the same.
I have an older laptop and my desktop and they both load fine.
I have tried all suggested options on the blizzard website & elsewhere (remove addons, WTF, reinstalled, reset router/network connections, tried connecting with it plugged directly in and probably some other things I cant remember).
I suspect it is some sort of connection setting/issue from what I have read elsewhere but I am at a loss what it could be.