USB devices that are connected to a computer may not work after the computer is idle for more than one hour Windows 7 or in Windows Server 2008 R2.
LastUpdate : Wed, 02 Mar 2011
Answer
Install Window7 SP1 or download hotfix Windows6.1-KB978258-x64.msu for 64bit, Windows6.1-KB978258-x86.msu for 32bit from Microsoft website.