Note: you need to setup correct video mode for PAL/NTSC machines (proper video/audio sync and vsync).
edit /boot/config.txt

for PAL version (50 Hz) you can supply this values:
720p mode:
hdmi_group=1
hdmi_mode=19
1080p mode:
hdmi_group=1
hdmi_mode=31

for NTSC version (60 Hz):
720p mode:
hdmi_group=1
hdmi_mode=4
1080p mode:
hdmi_group=1
hdmi_mode=16

See http://elinux.org/RPiconfig for more info.