may be try replacing the CR3032 battery on the main board.
And in addition, also try this procedure at https://discussions.apple.com/message/21807454#21807454 which is similar to what you have already done but worth a try.
Post your results for others to see.
yes... I wound up taking it to the shop - an expensive repair, essentially a refurbishing. The J&R tech guy tested everything, wound up replacing the logic board, video card, as well as the original DVD drive which stopped working a while ago... anyhow, it was costly and took two weeks, but was worth it - the machine now functions like a brand new unit! a very awesome and powerful machine, it justified the expense of refurbishing it to keep it going for a few more years, I hope!