If you have downloaded WIndows 10 You need to create a bootable drive.Then this guide is for you.
How to create bootable windows 10 usb drive:before proceding further you need to download windows 10 isoimage and poower iso.
Prerequisites:1.Windows 10 iso image
Step 1:Download and install power iso.Launch power iso Got to tools and click on bootable usb drive.
Step 2:Locate the place where you have placed windows 10 iso image.
Step 3:Select the writing method .In my case usb-hdd worked fine. and click on start.Wait till the writing is completed.Once it is done Safetly eject the disk and now you have a bootable windows 10 usb Drive.
1.Get into bios by pressing f2 or del or f12 at boot.
2.Set the first priority of boot usb drive.You dont need to worry what is no os is available in pendrive.If it does not detect bootable disk then it boots normally.
3.plug in the pendrive and boot normally.Proceed through installation procedure.It may take about 40 minutes for the installation to complete
Must read:Install windows 10 on windows 8 or 8.1