Updating your Pi
sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade
sudo apt-get install raspberrypi-ui-mods
HDMI not working
The Pi outputs a relatively weak HDMI signal. Some devices may not immediately notice the Pi's HDMI or may not do the negotiation. Setting the hdmi_force_hotplug=1 makes sure the Pi believes the monitor/TV is really there. You might also need to set config_hdmi_boost=4 or even higher (up to 9) if your display needs a stronger signal. If the display is a computer monitor, use hdmi_group=1 and if it is an older TV, try hdmi_group=2. Do not set hdmi_safe=1 as that overrides many of the previous options. Using a shorter or better quality HDMI cable might help. Make sure your Pi's power supply delivers 1A and not 500mA. If you see a problem with the red colour - either absent, or interference - then try a boost. However it might simply be that the display requires a stronger signal than the Pi can give.
Reset root passwd
In cmdline.txt, add the following at the end of the line:
Reboot. Remove the previously added part in cmdline.txt (i.e., revert to the original).
Reboot once again.
First stop for help: http://elinux.org/R-Pi_Troubleshooting