Windows 10: Install Windows 10 as dual boot without USB or DVD

See Windows 10 - Clean Install - Windows 10 Forums

You need to boot the install media, not launch setup from a running Windows.

Step 7 enter your Win10 MSDN key
Step 10 ... there is a custom install - I've done it.

You won't have to clean the drive , but the partition should be unallocated / unformatted.
Delete the D:\ partition you created (D:\ = primary = to be used for Windows 10 to install Windows 10)
either in the custom step or before you begin the install
Then select the unallocated space in step 10 (you can shrink it later if it's too big)

Good luck ... it's easy

 

I know it works this way. But I can't make install media. (This is work PC, and it doesn't have a DVDRW and we cannot use USB drives) :-/

 

Ok, beats me how you'll accomplish this then. If it's a work PC, contact your IT department.