How do i load my library from my nano to a new pc

You should have copied the library from your old PC first - if you still have access to it, see How to move your iTunes library to a new computer - Apple Support for information. If that's not possible, there is no way within iTunes to copy media from any iDevice to iTunes (with the exception of Store purchases on iOS devices) - iTunes sync operations are fundamentally one way: computer to iPod.

There are however, ways to accomplish what you need (assuming that you can't simply copy the library from the old PC). See turingtest2's user tip on Recover your iTunes library from your iPod or iOS device for information on various methods and 3rd party tools that can be used to recover content from iDevices to iTunes. You can also achieve a partial recovery (media only, possibly without artwork), as follows:

• Run iTunes with your iPod not connected, select Edit > Preferences > Devices and check the Prevent iPods, iPhones, and iPads from syncing automatically box
• Connect your iPod, select the Summary tab and check the Enable disk use box
• Exit iTunes
• You should now be able to see your iPod as a disc drive in Windows Explorer. Make sure that you've configured Windows to show hidden files and folders (Organize > Folder Search and Options, View tab).
• Open the iPod_Control folder on your iPod, and copy the Music folder that you'll see there to your desktop
• Still using Windows Explorer, right click on the Music folder just copied to your desktop and make sure that both the Read-only and Hidden flags are cleared.
• Run iTunes, select File > Add Folder to Library..., navigate to and select the Music folder on your desktop
• The previous content of your iPod should now be added to your library. Any songs/albums for which you'd previously used the Get Album Artwork function will no longer have associated images, but these should be easily redone.

This should be regarded as an "emergency" procedure only. There's no excuse for not maintaining an up to date backup of your iTunes library (as with any data that you value) - computers, and in particular hard drives, always fail ... you just don't know when it's going to happen. See another of tt2's user tips - Backup your iTunes for Windows library with SyncToy - for a suitable/recommended method. Although cloud-based backups are the way things are headed, its probably still simpler to use an external hard drive - this may not be as high-tech as using the cloud but is more robust, at least as far as not having dependence on an internet connection.