I have had this happen in the past. If the drive is not lined up perfect when being put back together, it will be misaligned and wont accept disks in. When it didn't accept them in, it would click and cluck trying to take the disk in but since it was out of alignment it never goes in.
One good question is.... did it accept disks before you took it apart. If it did, then it should be a simple fix. If not, then it could be a previous person working on it, or the drive's circuitry is messed up.
One fix is to take the drive apart and try to get everything lined up and happy again. It takes a few times to get it right, but you should be able to look at photos or videos of opened drives to see where everything should be.
Worst case is to replace the drive even though I'm pretty sure it isn't bad.
Good luck, and let us know if you get it working.