Don't mess with things you don't understand. For example, if you don't know how to get to the Windows Registry, you probably don't have any business messing with it. Yes, there's a time to learn about it, but it's best if you learn about such things after you've done a backup, when you don't have any kind of time limit for getting the system working again if things do go wrong, and when you have access to someone who can fix it if things go totally toes up. Plan for problems. Just like you check the oil regularly in your car, do regular backups of those files that would be most difficult or impossible to replace if you had a problem.
CD burners are cheap and blank CDs cost pennies.
Get a CD burner and blanks, and a CD with your documents, web browser bookmarks, contact files, email files, data files from your accounting program, etc. Windows machines crash. The operating system gets corrupted. Just expect it. I rebuild the operating system on our PCs at least every six months or so.