hi, you're using the correct method. i dont know to what extent the version of DrmClien.DLL (it ships with Windows Media Player!) is important but what you could do is trying to download and play FREE public DRM-protected *.wmv-files so that we can compare.
my undrmed videos from the BBC iplayer TV webpages play perfectly well!
( maybe it is time to reinstall your old Windows for the sake of ensuring a CLEAN windows. Clean from dirt, bad codecs, or other "influences". )
Go to
http://www.bbc.co.uk/iplayer/tv
and download some videos in Windows Media Video format. (if you dont live in the UK, then use proxy or vpn.)