Why can't I put my songs from my iPod onto my computer?

"I wan't to put the songs from my iPod to the computer"

You can't sync or drag your non iTMS music back directly from an iPod to iTunes. The transfer of non iTMS content is designed by default to be one way from iTunes to iPod, the transfer of purchased tracks has recently been introduced with iTunes 7. However there is a manual method of accessing the iPod's hard drive and copying songs back to iTunes on Windows posted in this thread: MacMuse - iPod to iTunes

If you prefer something more automated then there are a number of third party utilities that you can use to retrieve the music files and playlists from your iPod, this is just a selection. Have a look at the web pages and documentation for these, they are generally quite straightforward. As iTunes 7 is just out some of these may not have caught up with it yet though I haven't experienced any problems with the Mac software I use.

YamiPod Mac and Windows Versions
iGadget Windows Only
iPodCopy Mac and Windows Versions
iPod Access Mac and Windows Versions
PodUtil Mac and Windows Versions
iPodCopy Mac and Windows Versions
PodPlayer Windows Only
CopyPod Windows Only

For more on the new function in iTunes 7 look under under File, "Transfer Purchases from iPod" which transfers iTMS purchases. A paragraph on it has been added to this article: How to use your iPod to move your music to a new computer

"".......without erasing my iPod"

If your iPod is set to update automatically you just need to take care when connecting back to your computer and an empty iTunes. You will get a message that your iPod is linked to a different library and asking if you want to link to this one and replace all your songs etc, press *No* (or "Cancel" if you are using iTunes 7). Pressing "Yes" (or Erase and Sync in iTunes 7) will irretrievably remove all songs from your iPod. Your iPod should appear in the iTunes source list from where you can change the update setting to manual and use your iPod without the risk of accidentally erasing it. In iTunes 7 Check the "manually manage music and videos" box in Summary then press the Apply button. Don't uncheck Sync Music it will be unchecked by default when you choose the manual setting: Managing content manually on iPod

Whichever of these retrieval methods you choose, keep your iPod in manual mode until you have reloaded your iTunes and you are happy with your playlists etc then it will be safe to return it auto-sync again. I would also advise that you get yourself an external hard drive and back your stuff up in case you have problems again. External drives are comparatively inexpensive these days and you can get loads of storage for quite a small outlay.