Check the troubleshooting tips on this page: Fixed! Windows XP SVCHOST.EXE 100% CPU High Utilization
According to Microsoft, “Svchost.exe is a generic host process name for services that run from dynamic-link libraries (DLLs)” (see full article here). The fact that you see multiple instances running is not in and of itself cause for concern, however what DLL’s each svchost instance is running may indeed be troublesome.
For example, on my current system, a check of task manager shows one svchost instance with PID 1044. This is running on behalf of “explorer.exe”, and I do indeed wish to leave it alone (I like my GUI). You do will want to check out the svshost PID entries and figure out exactly what they relate to.
Run a full system anti-virus scan, followed up by by an adware scan (AdAware + Spybot S&D; Hijack This; etc…). Follow this up with an anti rootkit program (Root Kitty; Root Kit Revealer are the two I’ve used). Once these are completed and any unwanted guests (so to speak) are removed, check and see what your CPU utilization is.
Of course, it’s always good to think back about what changes were made (like programs installed or uninstalled) to the system just prior to the start of your problem, as chances are it/they will have something to do with the issue(s).
I have had this problem in the past and it was Windows update causing the issue, basically I turned of Automatic updates, and the update service. Next I manually updated and put the latest service pack on and all was ok again.
All good things to check mentioned above. I just have this observation to add. Is one instance of the mysterious svchost.exe process showing up in Task Manager using 99-100% CPU with no applications listed and no explanation for the way it’s making everything else run so slowly as to be unusable? Check for printers, desktop shortcuts, or IE favorites pointing to servers or computers that are no longer there. Windows spends a great deal of effort trying to find stuff that isn’t there anymore.
One of the best tools you can have in your toolkit for diagnosing this issue is called Process Explorer. It was developed by Sysinternals. It is now downloadable from the Microsoft downloads website. The description of this tool is as follows:
Ever wondered which program has a particular file or directory open? Now you can find out. Process Explorer shows you information about which handles and DLLs processes have opened or loaded.