I have a DS3 with this problem too. Jumpering the CMOS clear does NOT make the overclock work.

I got it working once before through persistance. After it started working, it continued to work until I added a 2nd DIMM, then it stopped. I removed the 2nd DIMM but it still wouldn't go back to working.

After several days of trying I got it to work again today with 1 DIMM. I have a Celeron 2.53 ghz and a 7600GS video card. Today it started working when I set the PCI-Express speed to 115. Setting to 100 didn't work. The results when it works are pretty impressive, the Celeron went from 2.5 to 3.9 ghz stable.

Now I want to try my 2nd DIMM again, but I'm afraid to touch it and lose my 60% overclock again...