Give testdisk a go, see for example this tutorial. It is a terminal utility, so it might take some time to get used to it. But no one can guarantee that it will successfully recover anything, the deleted files stay on the disk only as long as they are not overwritten.
Do you have any idea why the files disappeared after reboot? One thing that comes to mind is that they might have been saved in /tmp, in that case I believe recovery would not be possible.
Regarding to which files you should recover, try all of them and see if you have any luck.