I have Debian. I want to run Windows on the same hard drive, but in separate partitions. I don't want to start my computer "DualBoot" (DualBoot is causing problems for the computer). what should I do? Can I press a button (choose Windows partition) at boot and enter Windows?
You can install it on a different drive and select the boot disk in the BIOS. That is a form of dual boot but you don't need Grub or similar to select the OS. It depends on why you want to avoid dual boot. You will still have the problem like that Windows sets the clock to local time, but that is something you can change.
A other option is to use a VM. It is possible to use a disk for your VM if you don't want to use a disk image file like VDI.