Once the error is onscreen, you're not going anywhere with that boot. To get the disc to boot without hitting the hard drive first, power the unit on, open the DVD tray, and drop in the EvoX disc. It doesn't matter yet if it fails with error 13 or not. Just close the tray with the disc in and power off completely. Power on again, but using the power button (not the eject button) and the Xbox will detect the presence of a disc and load that first, without checking the hard drive contents. EvoX should boot and you can then FTP in and see what's going on in C:.