how to install windows os to an Android pc

Solution
Generally not possible. Android usually runs on ARM chips (though there are a few x86 ones), and Windows on x86. Windows RT is for ARM, but thoroughly locked down.

There's also licensing to contend with, and MS doesn't sell RT licenses to end users.
If you have an x86 based Android device then it is possible... but most Android devices run on ARM which is not compatible with x86 software.

Something really popular is for businesses to buy up bulk quantities of x86 Chromebooks, and then use their VLA copies of Windows 7/8 on them. It gets them dirt cheap but decent hardware, and then they do not have to pay for Windows twice (once on the device, and once with the volume licence agreement)