When I try to sync my Ipod 5th gen to my comp uter, it keeps saying it cannot be synced because it cannot be found. Ive synced it to this computer before without any problems.

Just now, I hooked my ipod up to my computer to put music on it. But it will not allow me to sync. Every time I try, a box appears saying "The Ipod "Alex's Ipod"cannot be synced because it cannot be found" I have connected this ipod to the computer before without any problems except for right now. and it has not been connected to any other computer. help please