I don't have important Data on my W10 Machine's, just use it for Work and daily-internet usage..
1. should i only reinstall W10 when the OS can't start properly anymore, or something is changed by a Virus?
2. can Low-format kills a hard drivers sectors or other things in a Hard drive?
3. i dont know why i always reinstall W10 every Month
1. Troubleshooting should be practiced to determine what the problem is. It could be something simple, or it could be something you aren't aware of. If you can't discern if you need to reinstall the operating system you should definitely post your problems here at Bleeping Computer where you can get good advice.
2. You shouldn't format a partition which contains any aspect of the Windows installation. If you format a partition you will lose the data that was previously there.
3. Quit reinstalling the operating system. There are other options which can be run with in the process of running it will basically reinstall the operating system. A good example would be to perform a Reset. This will reinstall the operating system, it also has the option to save your personal files. The downside is that a Reset will uninstall any third party programs you installed. During this process a list of the programs being unistalled will be available. I would suggest copying this so you have this list.
How to perform a Reset.
1. Press the Windows key and the I key to open Settings. and the I key to open Settings.
2. Click/tap on Update & Security, then Recovery, then Get Started.
3. You will now have the option to Keep my files or Remove everything. Click/tap on the option you want.
4. You will now receive the message Getting things ready, Windows will list the programs which you will need to reinstall. You may find it beneficial to copy these programs for a reference later. When the list of programs is shown click/tap on Next.
5. You will now receive the message Ready to reset this PC, select Reset.
The installation will continue without any need to make any other selections.