I don't have this phone, but generic Android instructions should work fine. While the screen is on, press and hold the power button and choose reboot from menu (if no reboot, choose power off). Alternately, you could simply pull and replace the battery. If you want to do a factory (hard) reset, menu > settings > SD& phone storage > factory data reset. This will wipe the phone clean but not the sd card. When you set up the phone, entering your google account will restore your contacts and calender. You will be able to re download all paid apps in the market but you will have to find the free ones yourself. Gmail is saved on googles servers but other providers may not be and old sms messages will be gone (if you care). When you do a hard reset all the system files are restored to factory "fresh", so any corruption will be gone. If the problem still exists after a hard reset, it is likely there's a hardware issue. Good luck, pm me if you need more personal assistance.
