Problem: PC becomes virtually unresponsive at about the same time each week. You can move the mouse fine, and possibly Alt-Tab around a bit. Doing anything else results in a hang that lasts 5-15 minutes, at which point the PC will "unfreeze" for 10-15 seconds, then go back to being unresponsive.
Debugging is almost impossible since the computer only works for a few seconds every 5-10 minutes. Meaning you cannot realistically look at Task Manager or any other program to identify the offending process. This particular bug can take hours or days to sort out, 15 seconds at a time.
What you can do:
1. Set the following programs running while the computer is still responsive:
- Windows Task Manager (Ctrl-Shift-Esc)
- Resource Monitor (run "resmon.exe")
- Process Explorer
- Set Task Manager to "Processes" and "Show processes for all users".
- Set all programs to order processes by CPU time
If you can, set these up so they're always visible on a second/third monitor. Alternatively, set them up on another desktop (i.e. Dexpot).
By running these proactively, you will at least have the chance to identify the program/process that's gone crazy. Even if the PC hangs, the last good updates to these programs should tell you which process is taking all of your CPU time; all you have to do is make/keep them visible, which should not take too long.
Regardless, as the problem is (approximately) a weekly occurrence, you want to look for something that is scheduled to run weekly.
1. Antivirus scans are typically set to run weekly. Try disabling the antivirus scanning temporarily.
2. Windows Update is broken and is hanging while searching for an update. In this case, one of the scvhost.exe processes will be taking a lot of CPU.
Conventional wisdom has it that most of these hangs are the results of an scvhost.exe process that hosts Windows Update process wuauserv. The cause is a borked / broken Windows update, leading to a situation where the wuauserv ends up constantly searching for updates, hogging the CPU in the process.
This manifests as wuauserv taking excessive CPU time. This is visible in Resource Monitor if you select the right scvhost.exe (there are normally several) or Process Explorer. In Task Manager you will only see one of the scvhost.exe instances taking CPU, but you can't tell which underlying process is actually the culprit.
As Windows 7 is end-of-life and is unlikely to get any future updates, simply turning off the Windows Update service in Control Panel should solve any issues with wuauserv.exe. For other problems, you may have to kill the underlying offending routine, figure out what it was trying to do, and disable that feature/program permanently.
[Update]: This could be an early symptom of a failing hard drive. If your hard drive indicator light stays on solid, or nearly solid, Windows might be trying to use a drive that is not working properly any more. See this post for more details.