Aside from the PRAM, there's a SMC (System Management Controller) reset. Apple doesn't describe your situation as being fixable with an SMC reset, but it does no harm to try. It's described here: https://support.apple.com/kb/ht3964
Out of curiosity, does target mode work? (Hold down T immediately after powering up.) If it does - make a backup to another system, ASAP, and we know that at least some part of EFI is working properly.
Hard drive failure could account for the problem you're seeing, if EFI is trying to read from your hard drive and can't; it'll get stuck doing so, not reading keyboard input. Power up the machine while listening with your ear against the machine. Do you hear the drive spin up? Do you hear any odd noises (such as the drive repeatedly trying to spin up), or repeated clicking?
Try disconnecting the internal hard drive temporarily and trying to boot off a CD, USB key, or other external drive (verify the device is bootable on another mac if there's any doubt.)
Try swapping the internal drive with a known-good drive from another Mac laptop, preferably with the same version of OS X (note that it may not successfully boot the whole way, but at least it would rule out any non-drive issues). 10.6 won't boot your system, and 10.7 might not unless it's up-to-date with system updates (very new systems ship from the factory with one-off modifications to the OS to support that particular machine if necessary, and then support is rolled into the next OS update.)
Getting to the drive involves removing all the screws on the bottom plate and two screws that hold the drive in place. It will not invalidate your warranty. If your computer is under warranty, you should take advantage of that and bring the system to an Apple store or authorized reseller for diagnostics.
It won't hurt to re-seat the memory modules while you're there, though this is unlikely to be the cause. If you have non-factory RAM installed, replace the factory RAM (or remove non-factory RAM) temporarily to eliminate it as a cause. Make sure to properly ground your body before touching anything inside, and re-ground yourself if you move (say, getting up out of a chair.) At the very least, touch the case of the laptop before touching anything internal.
You do not need to replace the bottom plate to power up the system for short periods (ie testing), but be VERY careful not to place the computer on anything conductive until you do.
If you respond with an update, I will try to update this with additional info based on the update.