Sony Ericsson Xperia X10 USB Debugging Detection Issues
Install Sony Pc companion.Go to folder in which flashtool is installed mostly C:/Flashtool.You will find Drivers folder in which you will find Driver.exe click it select the driver for your device click install.

Windows will give you error select Trust the vendor. It is better to turn off your antivirus. 

Once installed enable usb debugging mode and connect