Files moved partially and the rest gone! I moved about 100GB folders of pictures from one external hard to another one.

In the beginning of the process the finder breaks down and didn't respond. None of the relaunch solutions worked!

So I restart my mac but now, the moved part exist on destination hard drive but the other part doesn't exist on origin hard drive!

The destination hard shows folder in gray color but expect one the others have zero byte capacity.

Is there any way I can access the lost part?
Before you transfer any more files or make any changes to either hard drive, run Disk Utility and repair the two disks.

Hopefully, that will recover your lost files. If not you could try a commercial product like DiskWarrior, Drive Genius, or Data Rescue.

Unless you do a destructive delete, files are never actually deleted and as long as you don't save anything else to the disks the files are still there and have not been overwritten. As a last resort a data recovery service could possibly resurrect your files.