this is how I solved it
I am also facing same problem and yes when I press volume down while plugging in, the orange light blinks once in 10sec but the device doesn't get recognized or nothing is happening on the device side.
I flashed a wrong recovery.img and that's it the phone wouldn't boot. If I connect to pc companion it just shows blinking orange light but is not detected. This is what I have found out
1. the phone is struck in a bootloop which drains all the battery -- Press the hard reset button at the back of the phone to break from this loop
2. Put the phone on charge for a while ( now it should at least show a steady orange led indicative of charging) as this is needed for software repair
3. Use software repair in sony pc companion for restoring stock android os. -- if the phone is not detected when you plug in while holding volume down key, then release the key once and again press and hold it while the usb is still connected (this worked for me)
4. once the phone is detected and repairing has started the process may fail in between and pc companion may say repair failed!(don't loose hope) -- disconnect from pc, press hard reset button again and repeat steps 3 & 4. ( the repairing process will resume and will be completed slowly)
Note: If your phone is struck at sony logo or is not fully switched off press and hold the power+volume up key together to first switch if off and then connect to pc companion
