It seems as though the problem is solved. I just called HTC, and they requested me to switch the phone off, remove the battery, replace it, switch on, and try. It worked. Amazing.
It reminds me of the four people who were driving downtown: a mechanic, electrician, plumber, and IT expert.
The mechanic said there seems to be a problem in the mechanics. The electrician said, it seems to be an electric problem. The plumber said: I think there's a leak. The computer man was silent. They demand from him an explanation and he said: I would rather say, we should switch off the ignition, remove the key, jump out of the car, lock the doors, remove the battery, reconnect it, open the car again, get in, and start it. It should be alright then!!