Jim's computer slow down to a crawl at the top of the hour. Leo says it could be a time based issue in Windows. Leo recommends rebooting it in Safe Mode and see if it still happens. If it doesn't, then something is running in the background that's causing it. He could also try another browser and see if that fixes it.
If that doesn't fix it, then he should look at Windows Services by pressing Windows Key + X. That will show him what is running on his system. Leo also recommends using SysInternals: Process Explorer and AutoRuns. They are free and will show him what tasks are running.
It may also be "cruft" slowing it down while the computer is indexing — especially if his hard drive is old. A new hard drive or reinstalling Windows will speed it up.