Week ago i tried to connect my Nokia N9 to my new formatted (Win7 x64) computer.Computer could not recognize the device.I installed all updates and tried again , not working ...

And also charger does not working at all.I sent my phone to Nokia Care and they fixed the problem.I got my device back yesterday.I charged my phone again and everything was fine.Then i wanted to connect my device to computer again and computer didn't recognized my device again.After that i tried to connect to charger , and it doesn't charge ... So i broke my N9 again it seems ...

I'm thinking that there is some voltage problem with my USB ports or something like that.I'm going to send my device to Nokia Care again and i don't want to have this issue again.What should i do , any suggestions ?