If it will not power on at all, you may be looking a dead main board. To preserve your data, you'll need to physically remove the hard drive and connect it to another computer (you can do this either by installing it to another laptop with a SATA port, via a USB adapter, or install it to an external enclosure and connect the enclosure to another PC, then back up the contents you need to the host computer).
At 3 months, as long as it wasn't purchased from anyone shady, you should be able to contact Sony and send the laptop in for service. They're liable to format the hard drive though (or even replace it), so be sure you back up what you need before shipping the laptop!