I had this problem before on "Safely Remove Hardware" icon disappearing. I was able to use this method to access the dialogue box:
Start -> Run -> RunDll32.exe shell32.dll,Control_RunDLL hotplug.dll
Right now trying to solve the problem where my USB display adapter is not working and not showing icon. But I think this might be a problem with the USB ports configuration instead of icon not showing up in System Tray.