File based disks lost after restart

[IWillAskAQuestion]

At first I wanna say that I'm (quite) new to Linux and Fedora.
Currently I have to use Fedora at school, but I'm running into some problems. To make things faster at school, I'm now trying to do the same thing at home using WMWare virtualbox.

Our task is to setup 2 file-based disks using 4 image files and loop-devices. I can create and mount and use and do whatever with them, but after restart they are gone. Also all physical volumes and volume groups I created are gone. I used /etc/fstab to automount them at startup, but it doesnt seem to work.

Here are the lines i added to /etc/fstab:
/dev/loop0 /mnt/isoimage iso9660 defaults 0 0
/dev/labvg/webhosts /var/www/vhosts ext4 defaults,_netdev $
/dev/labvg/vhd /var/vhd ext4 defaults,_netdev $

labvg is volume group, webhost and vhd are disks i created

[Lakshmipathi]

Though,I haven't added loop device on fstab. I think,It should be possible.
Googled out this link -
Loopback Devices in Linux

/dev/loop0 /mnt/crypt ext2 user,noauto,rw,loop 0 0

[IWillAskAQuestion]

My problem isn't adding loop devices to fstab. It works just fine.

mount -a

works like a charm and it gives no errors.
But after restart all physical volumes and volume groups are gone and i have to recreate them.
After restart mount -a gives me these errors:

[root@localhost ~]# mount -a
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
       missing codepage or helper program, or other error
       (could this be the IDE device where you in fact use
       ide-scsi so that sr0 or sda or so is needed?)
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

/dev/labvg/webhosts: No such file or directory
/dev/labvg/vhd: No such file or directory

Oh, i forgot to tell you that on loop0 is mounted a iso file. It doesn't automount it neither after restart.