how can I download windows 7 without a cd,I have the product key.
As long as the product key is legitimate you can do the following:
1. Go to Digital River and download the ISO file that is correct for your product key. NOTE: If your product key is pirated or black-listed (fake) it will not work.
2. Follow the instructions for creating a USB Key to use to install Windows 7, found HERE .
I will say this again, if the product key is not genuine/pirated/black-listed, it will not work correctly. Do understand that we do not directly support those types of piracy and we will not do so.
I'm giving you the benefit-of-the-doubt since the information I gave you requires a valid key anyway.