Are you using Windows XP?
If so, go to Start>Run> type 'MSCONFIG' (without quotes). Select the Startup tab, and you'll see a list of apps that load up by default when you boot your OS. Make sure everything beginning with NV is selected (or just select everything in the list if there no already).
Or, simply right-click on you desktop, select nVidia properties, select the Tools tab and check the 'show up in taskbar' tab