Having trouble getting the "new mail" sound to play on my Win7/64 desktop.

Never had problems with v.6.* on XP, or Vista; have no problems on Win7/32 laptop.
However, on my Win7/64 desktop, there were only a couple of default, pre-installed Windows wav files that would work for version 6.*. (The majority of my archived wav files and "new" ones would NOT play.)
Today, I had to restore the machine to factory image, so I installed MWP2010 1.0.10, instead of 6.5.4.
Alas, same problem.

None of the really cool wav files posted to the related threads here at the forums seem to work in this environment (even though the same files play just fine on my 32-bit Win7 laptop).
Even plain "sound effects" stored under C:\windows\media don't tend to play properly in MWP in the Win7/64 environment.
All of my drivers are current, and there are no other audio problems with the system.
Research on the net suggests that Win7/64 somehow handles wav files differently in some way (that I don't understand).
So, can anyone help?

TYVM,
daledoc1