Boot from USB drive on a Macbook Pro with Windows 7 installation
Unfortunately, A1286 is not enough information to identify which particular MacBook Pro model you're using, as that's the part number for the 15" unibody case, not the computer.  All non-Retina 15" MacBook Pros made between late 2008 and mid-2012 carry this number.

However, it's a good bet that the model you have cannot boot anything from USB other than the MacOS itself.  Since these models have optical drives, the only Apple-supported way to install Windows on them was to do so from a Windows DVD, and thus the firmware didn't support Windows USB install sticks.

Since you're trying to boot KillDisk, I'm guessing you want to destroy the drive for the purposes of selling or junking the laptop.  Fortunately, you have several options available to you:

Option 1:  Boot the machine to Internet Recovery and use Disk Utility to wipe the drive.  This is only supported on 2010 models and later.  You can access it by holding down CTRL+Option+R immediately after hitting the power button.  This is the option with the least amount of hassle if your Mac supports it.

Option 2:  Extract the drive from the computer and place it into another computer (PC or Mac doesn't matter), and use whatever tool you want to wipe the drive.  Unlike Retina 2012 and newer Mac models, the hard drive in yours is easily removable.  This is the option with the least amount of hassle if you're comfortable with opening up the computer's case and handling components.

Option 3:  You can make a bootable MacOS USB drive.  You'll need another Mac to do this, of course.  But you'll be able to use Disk Utility to wipe the drive once you've booted from it.

Option 4: Connect to another Mac with a FireWire or Thunderbolt cable and boot the machine into Target Disk Mode by holding down the T key immediately after hitting the power button.  The computer will then show up as a removable drive on the other Mac, and you can use Disk Utility from there to wipe the drive. This one is probably the most problematic unless you've got a FireWire or Thunderbolt cable lying around (probably not).



Just FYI, The "boot chime" is one of the defining characteristics of a Mac, and has been present in every model ever made until Apple (curiously) got rid of it in their 2016 and later models.  You should be hearing the chime as soon as you hit the power button, before the OS begins loading.  The only reason you wouldn't hear it would be if the volume were all the way down and the setting was saved that way in the P-RAM.  But the fact that you can't hear it shouldn't affect your ability to use the various startup keys that Macs understand.

You can reset the P-RAM to the defaults by holding down Command+Option+P+R immediately after hitting the power button and you should be able to hear the chime again.  I would recommend doing this anyway, because if you're selling it, the buyer would expect to hear it.