I had something similar happen to me with my Helix LT. Worked fine for months in my studio, took it out to play for some services at church as its first use at a "gig". Thursday night rehearsal, everything works/sounds great. Was traveling for the next two days so left it in the backpack inside my house, never uncased it after rehearsal. Come back Sunday morning for run-through, plug into the exact same power source (surge protected) and XLR to FOH I'd used before, flip the power switch and ... nothing. Tried different power cords, different outlets, etc. to no avail. Got it back home to my studio and confirmed it was inop. Luckily under warranty, so replaced with no issue or hassle. Great lesson for me to be more diligent about backing up as I've gotten to recreate most of the presets I'd made. Hope you can get your issue resolved.
