USB Debugging should be ON and then,
Try to reset the adb (DDMS Perspective --> Devices Tab --> Small
Triangle on right side(Last option) --> Reset adb)
The drivers are here:
http://developer.sonyericsson.com/wportal/devworld/downloads/download/dw-x10drivers?cc=gb&lc=en
Use adb devices
from command line to know if you've got the phone connected correctly.
Still have a problem then I have read a solution which says -
- From the device-manager, got the hardware-id of the device that
failed to install (under details, you can get the hardware-id, in my
case these Hardware-Id's were listed:
USB\VID_0FCE&PID_612E&REV_0224&MI_01 USB\VID_0FCE&PID_612E&MI_01 I
then opened the inf-file (sa0101usb.inf), and under the sections:
[SEMC.NTx86] and [SEMC.NTamd64] I added a new entry with the new
key...
i.e. -
%CompositeAdbInterface% = USB_Install, USB\VID_0FCE&PID_612E&MI_01
Then installing the drivers worked like a charm...
More POSTS for the solution can be found at - eclipse-dont-recognize-my-sony-ericsson-xperia-x10.