Custom pc, no DVD drive, only have mac computer

[Nick_is_my_Nickname]

I need to install win 7 through bios and all I have are mac computers. My pc has no optical drive

 

[popatim]

Purchase a usb flashdrive, 4gb is large enough, and then use it and your mac to create a bootable win7 installation flashdrive.
Once you have (downloaded or created) your win7 install ISO file you can then use Bootcamp Assistant to create a 'Windows7 or later installation disk' out of your usb drive (Dewtination drive); Click Choose and browse to your win7 iso file and then Next to begin.