Xbox Black Screens When I Upload A New KV

I got a new KV today, but when I try to flash it (I've used J-Runner, and Flash360) it causes my Xbox to Black Screen with on the middle light on the Power Button lighting up. It stays like this until I flash my stock NAND through Xell.

Any help?

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I'd do that, but I've seen stories of Stealth Servers stealing your KVs to sell as Shared. Don't know if they're true or not, but I really don't want to take the chance!