Apple 3 watch
I have an Apple Watch 3 that I haven’t used in awhile. I tried charging it. It charges for an hour now but won’t turn on. I’ve tried doing a reset and the apple logo just flashes at me. Is my Watch completely dead?
Apple Watch Series 3
Question marked as
If it hasn't been used in a while, meaning an extended time and it wasn't charged on occasion while not in use, the little Lion battery depleted and when Lion batteries remain depleted for an extended period of time, they usually cannot be brought back to life.
I'd guess your battery has no life left. You could pay Apple for battery service (which really is a full watch replacement, with a refurbished, but same exact model and color watch), but honestly, given the age of a Series 3 watch and the fact it cannot run the newest WatchOS and it's often very difficult to even pair a Series 3 with newer iPhones, it to me, wouldn't be a good investment.
I'd give serious consideration to buying a newer, more modern Apple Watch.