right click the start button and click explore.
have a look in C:\program files and look for the quicktime folder.is it showing here?
in that folder look for quicktimeplayer.exe click it.does it open or give the same message? if still getting an error try safe mode and try to uninstall it.
restart the computer and keep tapping F8 or f5 and select safe mode from the list.
try uninstalling via add remove progs here.delete any folders left behind after install.then restart in normal mode and install you downloaded veresion.