Sony Ericsson T600 hard reset via firmware update
Download PC companion and install
Install PC companion on your PC computer. Follow instruction. For firmware update you need a USB cable.
After your phone connected press Start / in Support Zone

You can also use Sony Ericsson update service tool

PC Suite is out of date use PC companion software
If nothing works: As last resort do a Sony Ericsson phone repaire with PC Suite. After installation Select ----> TOOLS > PHONE REPAIR
Download PC Companion for your phone

http://www.sonyericsson.com/cws/support/softwaredownloads/detailed/pcsuite/aino?cc=gb&lc=en

