Mmm, a quick "silly" question that I ask in all kindness as a double check
"H:" sounds like one of the default drive letters that are used by network admins for the users home directories for users on a file server. I suppose that H: a physical drive in your case so you're not trying it at work for some reason and its a network drive? Windows 7 does not like to run executables from network drives that could give weird problems like this (and awful performance of course
).
Another thing that I would recommend is to not install any games (or Steam) into the "program files" folder as the UAC in Windows 7 is a bit picky with that folder if the games are trying to change the contents in that directory and not by having volatile data in the %appdata folder that is recommended...
So - if "H:\Program Files" is your %ProgramFiles% directory I recommend installing Steam to another folder. But I guess you only call it that yourself to spread large installations to another disk to not clutter the "real" C: folder? Any way - I like to not use Windows "reserved" folder names myself as that in some rare cases can make weird stuff happen...
/mazex