Windows 7 Help

I'm having issues with the Task Scheduler. I was trying to change the default time Defragger ran, and have been having trouble ever since. Basically when I go thru and set it up, it says the task is scheduled and set, but when I restart my computer and go back into Task Scheduler, it says the tasks no longer exists. Sometimes it will say that the Task Scheduler service is not running, but when I check in Services, it is set to Automatic and listed as Started. This started a day or two after I ran C Cleaner for the first time, and I think it may be related based on this thread: http://forum.piriform.com/index.php?showtopic=22226. I tried the fix suggested in that thread by deleting the TaskCache files in the registry, but that didn't help. The only thing that came out of doing that is it erased all the default tasks that are scheduled automatically by Windows. I've got the System Restore turned off, so I can't just go back to an earlier point. So, a few questions:

1. Are those default Windows tasks set in the Task Scheduler critical/important? Should I worry about trying to get them back?

2. Is it possible to install individual components from my Windows 7 install disc, i.e., could I just reinstall the Task Scheduler without having to completely reinstall Windows?

3. Any other suggested fixes/insight would be appreciated. Anybody else heard of this or something similar happening?