Korg DW-6000

How to reset my good old DW-6000.
I want to have the original Sounds.
Please HELP me.

Hm, that's an oldie now! I don't recall the exact button presses for that one, but most synths have the original presets lurking around in the ROM, which can be recalled when you turn the box on while holding down 2 or 3 switches. I'd say dial up korg.com and leave an e-mail for the tech section. They'll be able to tell you what's what there.
Better yet, if you're looking for some new sounds for der wunderbox, kidnepro.com in NY probably still offers some data cassettes from that era. They cover the DW8000 and Poly-800, so your chances are good there. They should be able to give you that same info. Such things are lurking around in a LOT of old file cabinets....! Try e-mailing kidnepro@aol.com for details.

I don't believe the DW-6000 can be reset to factory sounds (I'm assuming this since the DW-8000 can't do it). I think you'll have to do it via the cassette interface or sysex dump.