You can only Sync to One iTunes Library at a time.
tjmommy2813 wrote:
I just got a new pc
From your OLD computer...
Copy your ENTIRE iTunes FOLDER to an External Drive... and then from the External Drive to your New Computer..
Full Details Here > http://support.apple.com/kb/HT1751
tjmommy2813 wrote:
...I can not remember how to sync my iphone to my pc ...
Make sure your new pc is Authorised
http://www.apple.com/support/itunes/authorization/
If you do not have access to the iTunes Library on your Old computer... or its Backup...
See these 2 Links...
Recovering your iTunes library from your iPod or iOS device
https://discussions.apple.com/docs/DOC-3991
Syncing to a New Computer...
https://discussions.apple.com/docs/DOC-3141