Every now and then I'll find that Explorer is using 25% of my CPU usage. The only way I can think to stop it is to end the task and run it again. It will usually take several hours before this occurs so it's not instantly repeatable. It may have something to do with one of the background processes that Windows 7 likes to do when nothing is happening. On the other hand it has occurred whilst I've been playing a game. Does anyone have any idea what it could be or how to track it down?
Sounds to me you installed crapware on your computer, probably designed for XP, and it screws up your Win7 explorer. Check for that. You can use AutoRuns from SystemInternal (free): http://technet.microsoft.com/en-US/sysinternals/bb963902 to know. Once you run it, wait a moment for the list of things populates, once done, go to the Explorer tab. For reference this is what I have:
Turns out it was only when I opened one particular folder with a lot of things in, I think it's the same process that goes through a DVD when you put it in. Was doing it for ages but doesn't seem to be doing it now I've mentioned it