Connected to a pc, it was virus affected, then suddenly it started usb blinking (that is connected and not connected) and finally disconnected. From then the phone became usb dumb. No charging via usb port or pc connectivity. I have tried with several usb cable/pcs. Tried hard reset. Even being suspicious about hardware I tried to replace the usb port. But that was OK. But it gives a very low voltage to the battery charging pin in the phone like 2V where the battery is 3.7V. But the phone runs OK. Thanks for your help.