I had the same problem as you... but I got fed up and I ignored the fact that it would connect then disconnect (and stay disconnected), and tried flash tools anyway, and it worked... Just try.
Load the scatter file in flash tools, click Download at the top, then plug the phone into the comp (without battery).
Let us know if it goes through, stops, or gives you an error.
If anyone disagrees with my methods don't be scared to yell at me... lol.
edit* fyi when I plug my phone into my comp it doesn't show in device manager. What it does do is make the "usb plugged in sound", then the unplugged usb sound, then nothing. But, it does let me flash.
Load the scatter file in flash tools, click Download at the top, then plug the phone into the comp (without battery).
Let us know if it goes through, stops, or gives you an error.
If anyone disagrees with my methods don't be scared to yell at me... lol.
edit* fyi when I plug my phone into my comp it doesn't show in device manager. What it does do is make the "usb plugged in sound", then the unplugged usb sound, then nothing. But, it does let me flash.