Got a Humminbird 798 SI unit that worked fine up until the last trip.  Had a burst of short beeps followed by a distorted image on the screen and then the power just cut off.

Check my lines, battery, fuse, and connectors and they appear to be just fine.

When I try to power it up, nothing appears on the screen.  The lights on the buttons do however light up, but that's about it.

Would like to hear some inputs before I decide to ship the unit in for repair...thanks a bunch!!

I'd clean (sand) the contacts on the power cord, fuse holder and fuse hard - to bright metal. If this doesn't work I'd call.

If you've got a buddy with the same unit, you may try plugging yours into his boat, or vise versa.  From what it sounds like though, you may need to ship it on in.

Remove the unit from the mount. Carefully spread the power cord pins apart slightly so you can't even tell you did it. Re-install the display and see if it is corrected.

Report your results.