My phone is dead!

hi,first of all my English isn't very good,sorry for that. my phone (Sony Xperia S (LT26i)) is dead and i can't turn it ON it also can't keep his charge even sometimes it was charging. So i decided to change my battery. I bought a BA800 battery and change it myself according to a video i saw on YouTube. after all my phone doesn't start up even i plug in it to adapter. just sometimes the logo of a repair appears and after few minutes it dissapers. when i plug in it to electricity the LED will be red. i don't know what is the problem !?

a repair man said that a new battery is ruined. so he change to a new battery but it doesn't start again and he says that it most be flashed but he can't flash it!

i myself searching internet and follow up structures (download flashtool,installing drivers,download ftf,....) but now when i press volume down my phone doesn't connect to PC. before it i haven't such a problem, i don't know what i have changed! please help me. my phone doesn't start up anymore and i can't change usb debugging mode or mtp. in device manage has yellow trianlges on some part including MTP USB device,Android device(Sony AFBI interface,sony composite ADB interface,sony fastboot interface),61833 class buss device.