The problem i am facing when i am trying to install ftf file using flashmode is, my phone only stays in flashmode for few second and jumps out of it and shows opensemc logo and all process finished. And same thing with sony pc companion, phone shows up in it for few seconds and then it disconnect automatically.
If your drivers are loaded you should be able to go into recovery, mounts and storage, and mount the sd card with it plugged into the computer. It should mount and you can put a rom on the sd and flash.
If it will not mount then your drivers are still not installed. If ftf is the way you want to go then load flash tool and plug in the device while off holding volume down. It should recognize the device. It will not stay in flash mode long. Best way is set up your flash and once ready plug the device in. Hope you get it going again as I am sure you will. Just be patient