Questions about Medion Erazer X7843

First of all, I would like to ask what exactly you have changed? Because if you don't know what you're changing, then you should leave it alone. But not only that, it also makes it much more difficult to help... Further, one should know what you mean by "not starting".... Can the laptop be switched on? Do you have BIOS access? What error message are you getting? Try pressing F8 continuously once before Windows would start, i.e. during the boot process, then the Advanced Startup Options should normally be displayed. Also read the following article: https://support.microsoft.com/de-ch/help/12415/windows-10-recovery-options