Please go to Start > Control Panel > Add or Remove Programs.
In the top right, click the check mark by Show Updates.
If the following exists, please Remove it: Update for Windows XP (927891) << It must have those exact numbers)
Then, please restart your computer, and download/install this update:
Update for Windows XP (927891)
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After another reboot, let me know if your svchost.exe continues at CPU 100.