I had a similar problem with my Dell laptop, running Windows Vista 32. It runs all day in a dock (I am a self employed graphic designer), sometimes 7 days a week, and one of my worries about using a laptop all day (as opposed to a desktop with more space for cooling) was that it would overheat. Anyway, Dell guaranteed it, with 3 years full warranty so I went with it. I have been running it for almost 2 years and until last autumn never had a problem, when suddenly it would have the same symptoms as described of 100 percent CPU usage.
I went through hours of trying to sort the problem, my IT support couldn't fix it, Dell couldn't fix it - everybody pointed at somebody else, so I would basically work with the machine until it happened (usually after a few hours running) when I would then leave it for 20 minutes to sort itself out - basically, I had to live with it.
Then one day, for the first time with much maligned Vista, I had a blue screen! It happened a couple of times over the next few days and Dell support talked me through the problem, coming to the conclusion I needed a new motherboard. They duly arrived, replaced the motherboard, and then, whilst doing this, the engineer looked in the fan cooling area. It was blocked. When he blew it through, a great cloud of dust came out, and he suggested the problem was purely down to overheating. Remember, this was only to fix by blue screen - nothing to do with the SVC host.
Whatever - the machine has run fine since, and the SVC host problem has gone away. I'm not sure that there is a connection, and I'm sure many learned people will say there is none, but the SVC host problem only arrived when the machine had been on for a few hours and was 'hot'. I am not a techie, but I have used a computer long enough to know that the problem it flags up is very often not the problem at all.
In this case, it seems overheating was the problem.

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