You are probably looking at a total OS reinstall. If it keeps cropping up time after time that you have to step back to a previous configuration and you have made no configuration changes then I'd bet you have some sort of virus or malware action going on. You might want to get a good antivirus and run that although after you've been hit is the least preferable time to run a scanner.

I'd suggest that you invest in a large package of CD-Rs and start copying things to them. That problem sounds a lot more ominous than just a problem with the sim. One of these days a restore point is likely not to fix things and then you are going to loose anything you haven't backed up.

Good luck.

It's imortant to back up only the most important things, and reinstall atleast once a year!