You're saying that when you open File Explorer using the "My Computer" or "This PC" icon, your phone does not appear in the Devices and Drives section? Have you tried different USB ports on your computer? The problem may be the port, not the cable or the phone.
Also, have you installed the WP desktop app? I can't provide a link here in the "Ask a Question" forum, but I can give you directions for getting there.
1. Go to windowsphone.com
2. Scroll down to the section labeled Spotlight (left column, lots of large "live tiles").
3. 4th one down is Sync your phone. That's the one you want.
4. On the Get the Sync apps page, the one on the left "Windows Phone app for desktop" will work with Windows 7.
Also note that further down the page, in the "More Ways to Sync" section, the purple "live" tile to "Move stuff with File Explorer."
Forgive me if the step-by-step is too basic. Never knowing how comfortable people are with their phones or PCs, I try to give instructions my mom could follow.