didn't find this anywhere in the forums so I thought I'd post in case someone else has this problem.
Just installed two new installations and absolutely could not get the database to connect. Tried re-installing, changing passwords, removing and re-installing databases, etc.
Finally I checked php settings in Wampserver and realised that I had inadvertantly turned 'php safe mode' on. Turned it off and all worked well.
wasted almost an hour.