Sassafras, glad my suggestion helped.
Koshka, one walkthrough I found says it takes five or six tries at least to get the door open, so I wouldn't give up too quickly.
If nothing is working, then I would suggest that you check a couple of walkthroughs, just to be sure you haven't missed anything. Besides the one here at GameBoomers, there is one at
GameSolves and a
UHS Hint file .
As a last resort, try going back to your last save and playing forward again to this part, using a walkthrough. Sometimes that shakes something loose...