By default, on the HTC HD2, long pressing the End Key will bring up a menu where you can choose between several options, one of them being to Power Off your Device.
In certain occasions, you don’t want or can’t access the menu by long pressing the End Key so you need to take off the battery cover and perform a classic Soft Reset. You can now directly Soft Reset your Device by simply long pressing the End Key and you do that by replacing EndKey.exe in your Device’s Windows folder. For now, the installation procedure might be a bit tricky: you need to download the EndKey.exe.zip to your Desktop, rename it to EndKey.exe since it’s an executable and copy it to your Device’s Windows folder overwriting the original (File Explorer might not allow that but third party file explorers like Resco Explorer will do the trick). Hope to see an automated CAB’d version soon.
(Source: XDA Developers)