I recommend installing Shark007's Win7 codecs
both x86 and x64 versions and installing the latest version of MPC-HC.
You can also get a recent version that is preconfigured by Shark to work with his codec packs on the "Tools" page of his above linked to site. However, I personally prefer my own settings on MPC-HC. (Btw, I'm a big fan of MPC-HC also, but I'm using the x86 version until CoreAVC Pro comes out with an x64 version of their video codec which I use for H.264 MP4 files. Fortunately, Sharks tools also support the Core filter.)
Basically, for Windows 7, with MPC-HC open, hit "o" which opens the options menu. Under output, I use EVR cust pres. Under internal filters, I have most things deselected.
Then use Sharks settings tools (one each for x86 and x64) to select the video and audio filters you want to use for each file type or format. His settings tools make it very easy to play around with different settings till you find what works best for your particular hardware and software and file type in question.
One tip: Since his settings tools need to be "run as administrator" to make most changes, I recommend right clicking on the .exe of his tools and using the compatibility tab to set those files to always run as administrator. That way you don't have to remember to run the app as administrator each time you start it up.
The most likely reason you are not getting any sound is that you don't have an audio filter properly configured to work with the type of file in question. Again, Shark's settings tool makes this about as easy it can be to select various video and audio filters and splitters for use with the various file types.