Well, not to ask a silly question, but how about trying to connect using the old mysql library, instead of mysqli??? If that doesn't work, either, than you have a flawed installation. Missing stuff. If that works, then you may still have a flawed installation, but at least you know it isn't because you forgot to uncomment the DLL.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.