Full disclosure: I haven't worked on a Fire HD, so this is hearsay. That said...
The FireHD Volume and Power buttons should be very easy to repair. Both are located on boards that are attached to the rear case, and they connect to the motherboard via spring/tension contacts. See this picture, taken from ifixit's teardown, to see what I mean:
[image|562314]
See the back case on the right side? The silver plate on the top covers the power button, and the silver plate on the bottom covers the volume buttons. There's a flex cable coming from each that ends in 2 (power) or 3 (volume) gold pads. See them? Now look at the left side. Those pads line up with the spring/tension contacts mentioned above
So how to fix either problem? First, take the back off. You can take a look at ifixit's teardown [guide|18027|located here] to see the process but it's pretty simple - basically just use a thin soft tool like a plastic opening tool to unclip the cover, working around the device.
Once you get the cover off here's how you diagnose it:
1. You know the tension pads we mentioned above? Use something metal (I use metal tweezers, but wire or a screwdriver works too) to jumper them and act like a switch. The power button only has 2 contacts so that's simple enough - connect them together with your metal thing and see if it turns on. If not, there's something wrong with the board (= big repair). But it probably will work. If you're testing the volume buttons I'd guess it's 95% likely that you jump the middle pin and one of the others for volume up/down. See if that works. Again, if not something's wrong with the board.
2. Ok, so that worked. What's next? Check that the spring/tension contacts aren't flattened and are able to align with the gold pads on the switch flex cables. If they seem flattened bend the up so they'll contact. You can put the back (partially) back on to test.
3. If it still isn't working remove the screws holding the switch in place and manually hold the switch in place over the contacts and squeeze the dome switch. Does it work? If so, there's probably an issue with spacing between the button and switch. You might need to make a small spacer to fix it (scotch tape works well enough). If it doesn't work the switch is bad and needs to be replaced. The only place I can find it right now is on eBay. Others might know better options (I don't get Kindles to repair very often).
Hope that helps you out!
The spring/tension contacts aren't making contact. Take a look - do they seem pushed in and flattened? If so, pull them out a bit so they make contact. I'm guessing this is probably the problem.
2. The metal dome switch pad is