Well you should run disk utility from your install DVD and under utilities drop down menu. Repair Disk. See if this helps. Won't hurt to repair permissions if you haven't or don't after system upgrades.
If no help could be corrupt plist try deleting com.apple.systemuiserver.plist
then open terminal.app and copy & paste the command:
and return. This command will kill the process and automatically rebuild the menu bar.
Hopefully problem solved clearing out old cache.
- when I start up the computer sometimes the Menu Bar doesn't appear; I must click on the Menu Bar zone and it appears and works. It happens since I have purchased it.
This is a bug in OSx that comes and goes since 10.6.0. Not to worry, just click on the menubar and it will return.