.idlk files are the lock files that prevent more than one user from accessing a .indd file at the same time. It's not likely thathes files are renamed.indd files, but very likely they are just leftover remnants from a crash or force quit. Lock files are deleted when the associated file is closed normally. As long as the .idlk file is not in the same folder as the .indd file with it is associated it should not prevent opening the file. Rather than deleting all of these files (just in case I'm wrong) I suggest you gather them into a folder someplace for safe keeping, then try looking for the .indd files again.