It sounds like your phone is not being recognized by iTunes on a couple of computers after an iTunes update was applied. I recommend the troubleshooting steps from the article named:
iOS: Device not recognized in iTunes for Windows
Here is an overview of the troubleshooting to be done:
1. Update iTunes
2. Check the USB cable
3. Verify that Apple Mobile Device Support is installed
4. Restart the Apple Mobile Device Service
5. Verify that the Apple Mobile Device USB Driver is installed
6. Check for third-party software conflicts
iOS: Device not recognized in iTunes for Mac OS X
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Thank's a lot! - I don't know what exactly helped me - I also made a reset of the Sync Services (for example here: http://support.apple.com/kb/HT3783. But the important thing ist, that my iPhone and iPad are shown again in iTunes.