A little more info would have helped, O.S. Age; Manufacture, for example. You need to ascertain whether you have a partitioned O.S. If this is the case then you have only one problem, how to reinstate this on to a clean disk. That is the situation concisely. Try the following
Factory reset generic
Now, from a completely mains off situation, important, you’re ready to go. This won’t work unless you have a partitioned OS, so you’ve nothing to lose give it a go.
Go: - Switch it on, as it whines-up immediately and continuously tap F10. (This F number can be manufacture dependant) You must start from a power off situation. Until this action brings up on screen a selection of options. This is imperative; you must achieve this before proceeding. Unsuccessful first time, switch off and try again.
One option offered will be - Select “Repair your Computer”, click this. Follow the on screen instruction but the result you’re after is their top option a “Full Destructive Recovery” when presented go for it, don’t be shy, it might frighten you by asking twice.
Follow the on screen instructions and click start, and enter. All you can do now is to sit back and relax, go for a coffee, leave it well alone let it do its own thing, it’ll take about 30 minutes.
Don’t bother to install any drivers (e.g. printer) asked for during the run up as this can easily be done after you have your pc back, in your control.
After the event, and you’re breathing again, you’ll need to install. Your printer disk, a very long boring up date session, this is best done “automatically install MS up dates” over-night, on-line, while you sleep.
You now have your pc back as good as the day you purchased...good luck