Is it a two tow-hook system? Many G-103's removed the CG hook and replaced it with a dummy block. Was the re-installation proper? Look for an obstruction resulting in the nose hook reaching full open and not leaving CG hook sufficient movement to open. Check by removing CG cable (at hook), then actuating release system. Look for improper CG hook, improper installation, not enough cable movement at CG hook.
Hope this helps,
JJ