Networking IP address issue? Is the Mixrack set to a static IP address or dynamic? If it is dynamic, is it actually connected to a working network that has a functioning DHCP server on it?
If not, the boot process is going to be much longer as the MixRack will take an extended period of time trying to receive a valid IP address before it times out and completes the boot process. Simply changing the MixRack to use a static IP address will “fix” this extended delay if this is your issue.