New MAC-address, now I have no network-access

Solution 1:

Since your mac address have changed you no longer have an interface called eth0, this name is reserved for an interface with the "old" mac-address. The "new" interface should have the next free name (eg. ethN).

To see all the interfaces on the machine you can use this command: ifconfig -a

If you want to reset the name reservations for network interfaces you can remove the file /etc/udev/rules.d/70-persistent-net.rules and restart the machine (or remove/insert the device, though this is not possible in this case).

Alternatively you can change the interface-name that you have configured to what ever the new one is called by changing all occurences of the old name with the new one in the file /etc/network/interfaces