if u got solution to ur prob
drop a solution here
i am finding the solution too
Pulled a lot of my hair out, Seemed like that didn't help, So I reinstalled Windows fresh, And all drivers, Dumped Multiminer and went back to CGMiner.
Haven't got any other advice apart from that,, Sorry.
Hopefully it looks as though it's hashing fine again.
What happened at the point of the first big drop??? because its fine up till then, then when it comes back on its ok for a few hours then the next drop chops off the 10%. Find the cause of the first two big drops. That will most likely be the cause of the problem.
It was a power cut, Really not cool because last night was the biggest earner in ages, So i lost a hell of a lot.
All good now touch wood, Thanks.
Your problem was MultiMiner. I had this same problem a few weeks back. There's a bug in bfgminer so that every time the network difficulty changes (pool switches coins) the hashrate drops.