Force file deletion on Windows

You could use LockHunter to see which process is blocking the deletion of a file. It's a freeware tool for Windows (32 bit and 64 bit versions available) which integrates itself into the Windows Explorer context menu.

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 a reason. Unlike other similar tools it deletes files into the recycle bin so you may restore them if deleted by mistake.

_{(source: lockhunter.com)}

With MoveFile from Sysinternals you can schedule the deletion for next reboot or you could try to unlock the file with Unlocker.