Leopard problem

My iMac, which I upgraded to Snow Leopard, now has intermittent problems with USB devices. Memory sticks and other USB peripherals sometimes vanish from the Desktop, whether connected directly to a port on the iMac or via a hub. However, once they have vanished, disconnecting them results in a ‘disk was not ejected properly’ alert. On other occasions, trying the open the volume results in a spinning beachball cursor freeze, forcing me to switch off its power before starting it up again. Is this a problem in Snow Leopard?

There doesn’t appear to be any widespread or systematic problem with USB in Snow Leopard, although there are occasional glitches such as losing printer connection when ejecting a memory stick. The memory stick(s), the hub or your iMac’s USB port(s) could be failing. Demonstrate that this affects multiple devices connected via different ports, and power your hub before ruling out a hardware problem. Shed other USB devices in case they’re to blame – an old USB 1.1 peripheral, for instance. Next, check installed third-party software, particularly Startup and Login Items, and drivers for older USB devices such as a broadband modem. Restart with the Shift key held down to engage Safe mode, with non-Apple extensions turned off. Your Snow Leopard installation could have become damaged, either during the original install or the update to 10.6.1. Try downloading the standalone update from support.apple.com/kb/DL930 and see whether that helps. Note that you should never turn off the power to your Mac unless it’s a matter of immediate safety. Even a forced shutdown, normally effected by pressing and holding the power button, is preferable, as it shouldn’t leave software errors on your startup disk. Ensure you have a good, complete and recent backup and restart from the Snow Leopard install DVD. From that, run Disk Utility to repair your startup disk and then repair permissions on it.