I found this on another site and it should fix the problem
"....I also have the 1st generation ipod and was also missing the volume slider. Here are the things I did to get it to work again....
1. Power off
2. Power on holding the power and sleep buttons until I saw the apple symbol.
3. Unplugged and plugged back in my headphones.
4. Slider appears only when headphones are plugged in....."
Worked like a charm. Literally - plug the earphone into the jack. Turn the iTouch off using the sleep wake button (i.e hold until you get a red slider) and THEN when you turn it back on, WHILE the apple symbol is still showing, unplug the earphones and put them back IMMEDIATELY (Apple still showing). I heard a noticeable difference in sound as soon as I did this - and when the iTouch finished rebooting I went to music and there was the slider and the volume was back to normal! :-)
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when you say that the ipod works fine when hooked up to a dock, does that mean your volume bar shows up? What firmware ver is it? Does unplugging your ipod from the dock and unplugging the headphone make a difference? Have you tried a reset? First off, back up your ipod....
crwdns2934271:0crwdnd2934271:0 oldturkey03 crwdne2934271:0