Re: 7 years of music....gone :(
Greg nothing wrong with your existing iPod. Sounds like iTunes done gone and f'd up. Which is why I HATE iTunes with a passion :) All the iPods and the like are flash memory; when they go you'll know because you can't read OR write to them.
In the future once you get things fixed, while it's OK to copy and run stuff back and forth:
#1. Have a backup elsewhere (or at least manage stuff manually (check box in iTunes) so when you copy in from wherever you have that copy still in that disk/folder). Do NOT manage your "library" in iTunes. One wrong screw up or needing to fix iTunes and it's either all gone or all the metadata is shot/a major PITA to fix with a new installation.
#2. Consider a 3rd party transfer program without having to lug through iTunes each time. CopyTrans is a simple and free alternative when you just want to copy stuff over each time (but there are others).
[URL]http://www.copytrans.net/copytransmanager.php[/URL]
#3. As the extra step, safely remove hardware with Windows/USB. Seems to sometimes also be the reason stuff "disappears" since it can write quietly or not finish when you think it's done.