Restart your computer, go into safe mode options by tapping the F8 key. When the options appear arrow down to where it says disable automatic restart on system error and hit enter on it. Now when the system errors you will see a blue screen with a some information on it. Basically what we need is the stop code given at the bottom. Sometimes there is only information up at the top that might say unmountable boot volume, which means you have errors on the hard drive. Just let us know what the blue screen says.