If the button is correctly positioned it will be perpendicular to the screen, not tilted. Another test is whether or not you have a "half-press" feeling to the button, as a regular point and shoot camera would. If you don't get a "press half-way to focus" behavior, you may have a misaligned button.
If it is tilted in, as mine became, it's pretty easy to fix:
0) watch this video: Evo 4G LTE Teardown (Evo One X) - YouTube
1) power down the device
2) pry off the bottom piece (about 1/2 inch tall) located on the back
3) remove the 4 screws you find below
4) pry the screen out slightly and put into back in place and your button should be positioned correctly again.
5) re-assemble