Hopefully this will help
First of all use Windows 7 32-bit
Most probably it is a driver related issue.
Download latest flashtool and install all the drivers.
Also check weather you have automatic updates of Windows are ON.
Check in the device manager if all the devices connected are recognized.
When you connect the phone to PC does it show any message or feedback sound.
While using the flashtool use flash mode, also when asked to reboot in flashmode carryout the following steps
- Unplug the phone.
- Switch it off/ If already switched off make sure it is completely off no icon nothing.
- then connect the phone and switch on by holding both Vol Up and power button, you will see green LED glow.