[Q] htc desire not starting topic

My htc desire sv shut down on its own and now it isn't starting. It has around 50 percent battery at the time it turned off. I took it to a service center and they told me that the software is corrupted and a new software must be installed. I have installed (flashed) Roms many times but my device won't start. It just shows black screen. Is there any way I can fix my phone? It's not rooted and has stock ROM.
Thanks a ton.