Random keys on keyboard stopped working

I'm having problems with my laptop keyboard - specifically, some keys don't work any more.

The problem started three months ago - just three months after I purchased this ASUS K42F - when the left Alt key got busted. I cannot forget that moment because I was editing something important in Photoshop that required the use of such key. I didn't bother to do something about it; I still have the right Alt key anyway.

I was surprised when two days ago, almost half of all the keys in random positions didn't work any more. I haven't spilled any liquids on the keyboard, and I know nobody else has either because I always put this laptop in a vault when I'm out (privacy is a problem here). I've tried everything, from scanning for viruses and spyware to using compressed air, but nothing has worked. I hope someone can help me with this before I'll be obliged to visit the seller whose location is very far from mine. I still have the one year warranty.

Keyboards die. Laptop keyboards die faster. Mine died randomly as well, so I got a replacement from HK (although my laptop was out of warranty).

I'd first ensure the keys work in the first place. There needs to be a way to do this in windows, but i'm not aware of it.

Boot into a linux livecd start up a terminal, and install evtest - most modern distros have it. evtest will show an event whenever a key is pressed, so you can use it to check if the keys actually work. If they don't show up when pressed on evtest, well, its the key, and you will have to visit the seller. If it does, its a software issue, and you may have to investigate further