Repeated powering off and on, as we all do, causes temperatures to go up and down. Over time that can sometimes cause a connection to fail, so it's worth trying to unplug and replug the cables. Also get rid of all the dust that builds up inside the machine, being careful not to touch the electronic components. Since you get the VAIO logo displayed, your power supply is apparently working. If all else fails, you can remove the hard drive, put in a $30 enclosure and plug it into the USB port on a working PC. Of course, it the drive itself has bitten the bullet, that won't help either. I hope you've backed up any data you didn't want to lose!