No, updating the firmware (or re-applying the same one) nor formatting will void the warranty. While connected to you computer, Windows can format it for you (right-click on player’s icon in Windows Explorer).
It also could be hardware-related if it is not powering on except when connected to the computer. This sounds more like a battery connection issue. This was common with the old original Clip, but I haven’t heard of many similar problems with the Zip, so as I suggested before a call to Tech Support may be in order. If it’s still covered under warranty and determined to be defective SanDisk will replace it for you.
