The fact you can browse to it using the IP address suggests the underlying networking is fine.
To ping, go to start, type "cmd" in the search box, hit return...brings up a black box with a Command Prompot. Type ping x.x.x.x using the Receiver's IP address. It should give you four positive results pretty quickly. If there is a problem it will time out or take a relatively long time (100s of milliseconds) I don't think this will be a problem if you can browse to it. If your Amp is also able to access internet radio then there is nothing wrong with it's network interface. Sounds like a Windows Media Sharing problem or WM Player itself.
I always found WMP media sharing a bit of a pain...Jamcast is better!
Go to Start, Network, is your amp there? If it is, double click...that should bring up a WMP sharing dialogue box...is this set the same as your wife's PC? Check the settings and make sure music and pics (and video if you want) can be shared.
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