Wi-Fi sync not working !

Hi, i do exactly everyone is saying,(turn on the sync over wifi in itunes) and syncing works...but I have to leave the cable connected to both my iPod Touch and PC....but as soon i disconnect the cable the sync button turn grey and i cant sync,syncing stops... the ipod tab in itunes dissaperes...so basiclay...when i go to setting and itunes sync over wifi...sync button appears only while my ipod is connected and when i dissconnect it it says..that my pc is not avalible....,When its syning and i unplugg it out of the laptop...syncing stops... please help me thanks!