LockHunter

Shows processes locking a file or folder
Gives you detailed information on the process
Allows to unlock, delete, copy or rename a locked file
Can delete a file at the next OS restart
Allows to kill the locking process
Allows to remove locking processes from hard drive
Can unload DLLs from processes
Integrates into Explorer menu
It deletes files into the recycle bin, so you may restore them if deleted by mistake
Supports both 32 and 64-bit Windows

It is a free tool to delete files blocked by something you do not know. LockHunter is useful for fighting against malware, and other programs that are blocking files without reason. Unlike similar tools, it deletes files into the recycle bin so you may restore them if they are deleted by mistake.