In the early 1990s, a client using the venerable Cadzow Debtors Ledger Package for MS-DOS decided she wanted to “undo” some recent transactions by restoring a backup. So she set about it, and half-way through decided that maybe it wasn’t the right thing to do, and cancelled the restore, leaving a data set on her machine which was half from the backup and half from the live set — problem enough. But then she panicked and did a backup … over the same disks. So now she had two perfect copies of a total mess!
The moral of the story is not to panic if you have some sort of problem, whether it's a label stuck in a printer or a server that won't start. Many problems have relatively simple, albeit non-obvious, solutions.
Modern editions of Windows have all sorts of in-built “repair” and “system restore” functions which can be helpful in some, but only some, circumstances. So there's a great temptation for inexperienced users to let Windows perform all sorts of repairs or do roll-backs, and these can have unintended consequences.
It's also worth knowing that the vast majority of programs on the Internet which supposedly fix problems with drivers, registry, performance, malware etc are either useless, harmful or borderline scams.
Additionally, the Internet is awash with all sorts of advice from amateur experts to confused users to reformat their machines or fiddle in the registry. These should be avoided.
So it's really important that you take some advice about a problem before diving in or experimenting.