Q: My MacBook adaptor stopped working so I used my roommates. Now hers doesn't work after just one day. What happened?

Hello, cherilyn.  

Thank you for visiting Apple Support Communities.  

I understand that a couple MagSafe adapters will no longer charger a couple MacBooks.  Here are the best troubleshooting steps to go through when experiencing this issue.  

Apple Portables: Troubleshooting MagSafe adapters

Cheers, 

Jason H.