If the reset with switching to unmanaged does not work you can connect with the terminal and erase the flash file.
I was trying to create a test network with the 2808 to a router.  I put all ports into a VLAN and now I am unable to connect to it either directly or through the router.  I was wondering if I could manually reset the device to factory default without having to go into the GUI because I am not able? J
Locked out of Switch