Both those macros should work as intended.
#showtooltip
/cast [@mouseover,help,nodead] [] Power Word: Shield
The only reason i could see them not working is if you have them bound to mouse keys (eg mouse 4/5) in which case they wont fire over unit frames because unit frames eat mouse clicks; you need an addon like Clique to get around that restriction.
You could also further enhance their functionality if you want: