How would one deal with a SONY VAIO laptop that doesn't power up? When the power button is pressed (with AC adapter connected) the laptop makes a few crunching sounds for a couple of seconds and then goes quiet, except maybe for a fan. No sound, no boot. The power, wifi, and battery charging LEDs are on. The power adapter outputs about 20V, so I believe it is okay. It had always worked without a single problem before. Could anyone suggest where to start troubleshooting and what potentially could go wrong: hard drive, connection, fuses? Would greatly appreciate any help. Thanks.

Is the machine even getting to the POST and splash screens at all, or simply dead ?

It shows no POST screen or anything. It usually took a few seconds to start seeing POST messages. It goes dark and quiet after a second or two now, only three LEDs are on.

Well, I pushed the power button again. Again, the LEDs were on, a few crunching sounds and that was it -- no POST screen. Then I held the power button for 60 sec and disconnected both AC adapter and the battery, because this was the only way to shut down whatever had managed to turn on. After reconnecting power cord and battery, I pushed the power button, and the laptop went through the POST and started booting up as usual. When the system was almost up, the machine went dark and quiet again. Does this behavior suggest a faulty power cord or malfunctioning battery or anything specific?

It sounds like you could be having a hard drive failure. Did it say anything on the screen like "boot windows normally?" Or any other messages?