my sisters computer which is a dell and is fairly new, when they try to start it up, it will beep 4 times and the fans turn on but then it just shuts back down. Last night they took it over here for me to look at and I just used my monitor, keyboard, and mouse and it started up no problem and everything was working fine. Figured something must have just come loose or something so went through and checked that everything is tight and sent them on their way. Well they got it back home and went to turn it on, fans start, then it beeps 4 time and turned off again... whats going on?