Be careful not to be fooled by others or by your own brain that may see causality where there is none.People try the weirdest things, then they get all their icons and conclude sharply, but wrongly, that whatever they did solved the problem.Check your Startup folder and the starter registry entries through Start, Run..., type: msconfig, press Enter, to check whether the programs are really started at system start, or use Task Manager (Ctrl Shift Esc) to see whether the processes are running.A particular and special problem is that only the sound volume icon disappears, but the others are there. But first read the chapter "Other known causes" further below for some specific symptoms and solutions.Thus I receive hundreds of emails, detailing ever more different solutions to the problem, each of which has been tried and worked on one computer.
If, however, other systray icons disappear as well, then you should first skip this chapter and continue with the next.Combined with an unfavorable Windows API message this causes the problem, which befalls many heavily loaded computers that don't have ultra-fast hard disks.Changing the timeout to one minute and removing the unwanted message solves the problem, and in the Complete solution comment user depassp has perfected the procedure of patching shell32to solve the problem, at least until a new version of that DLL is delivered by Microsoft that re-introduces the problem and requires another patch session.(By the way, don't mistake UPn P for Pn P, Plug-n-Play, which is mostly a different thing.) Microsoft has not taken notice. Some users report successes with various changes that influence the boot and logon timing, but these changes do not reliably solve the problem.Often they make the problem occur less often though and make it bearable.In this case the main solutions below will not work. There are a few other problems that can cause similar behavior and can mislead you into believing that they are the same problem.If you are not sure, read the entire article first, because a few more are described later.In any case, please make sure for now that you haven't activated that setting.Right-click the task bar, click on Properties, uncheck the last check box.In fact, exactly this has happened around July 2010, but the solution is already here: Offsets for NEW 6.0.2900.6018 file by mcrealize, corrected by Tea Rex Unfortunately patching a system DLL is not an entirely simple procedure and can only be done with a certain minimum of computer handling experience, but this is the best we can offer for now.A few special problems concern the Task Manager and its systray icon only, the green one that dynamically shows the CPU load.