when I was instaling something my phone was sudenly switched off.

Most likely the system software has become corrupt.

You can perform a factory reset with bootloader which may fix the issue.

Follow these steps in order to boot the bootloader:

1. Press and hold both Volume down button as well as power button until the screen goes completely black.
2. Once it is black release the power button only. Do not release the volume down button.
3. You will be booted into the bootloader mode.
4. From here you can select and go into fastboot mode or recovery mode by navigating using the volume up or down. Use power button to make a selection.
5. Select fastboot USB if there is no factory reset / wipe data on the list.
6. If you selected fastboot check for a factory reset / wipe data there and select that option.

If the factory reset procedure does not get you out of a boot loop, then you will have to download the firmware that corresponds to the RUU code which you can check via fastboot on the phone through ADB software while the phone is plugged into your computer.

More instructions are found here on how to restore the system software on your phone:

http://forum.xda-developers.com/showthre...

In my opinion there it's just too complicated to restore system software on HTC phones when compared to LG, Sony, Samsung, iPhone and many other brands.