Windows 7 Windows Experience Index gives different subscores each time I choose to re-run the assement.

How are you running WEI? I agree the scores may be different when run at idle compared to fully loaded. But if you test it several times in a row, under the same load conditions (programs performing tasks - not just sitting idle) the scores should not change each time. Is that what is happening?

You need to run some programs while running the WEI, or disable any energy efficiency settings. Of course, without you specifying your system specs, we can only guess if your score is normal or not.