I can´t sync my iPod 3rd Generation with iTunes library

Hello, I´ve been trying for a while to sync my iPod with my iTunes library on my PC. It does show up on Windows as a drive and iTunes seems to know there is a device plugged in but then a message appears: "iTunes could not connect to the iPod touch because an invalid response was received from the device" I´ve tried several solutions, including: restarting the iPod Service, restarting the Apple Mobile Device Service, emptying my Temp directory and restarting and changing my device´s Drive Letter. On rare occasions, when I give it another try, I manage to get the iPod recognized, but when I enter the iPod menu, the sync button appears grayed out or if I can click it and attempt to synce the iPod, it seems to happen in the computer, but no changes are made on the iPod. I´ve tried syncing only music and only "selected music and tracks" but no setting seems to be transmitted to the iPod. The iPod shows the "charging" icon but never the "syncing" icon. I hope somone can help me. I have also tried syncing over Wi-Fi, and in the iPod, I can see the Pc but it appears grayed out.

And, to my outrage, random songs have been dissapearing from the iPod randomly. It sounds weird but maybe it is because of iOS 5. I have an iPod 3rd Generation and iOS 5.1.1 (9B206). Both iTunes and my iPod say my software is up to date and maybe the iPod is too old for further updates but I only want to get my new iTunes songs into my iPod. Please somebody help me. Thanks very much!