I have the same issue.
I organized xperia light rom for our xperia c, I flashed it from custom recovery. Phone is completely dead now.
There is a just red light, phone does not go into download or fastboot mode. Pc Companion, Sony Update Center, Wmshua Flashtool do not recognize the phone.
Any suggestion with that?
I don't have warranty, my last option is to pay money for technical service.