This is one of those things, maybe tidbits of info that I think are handy to have stored somewhere... the 2nd part I got lucky & stumbled on using Google, but when I tried to find it again because I'd forgoten to bookmark it, I couldn't.
When you start win7 you may someday find some of the tray icons are missing when you click the Up arrow on the Taskbar [just to the left of the Action Center flag]. It's not that uncommon of a problem, & the cure is:
1) if it's not set this way already, open Windows Explorer, go to the Tools menu & click Folder options -- click the View tab in the window that opens, and set it to Show hidden files, folders, and drives; uncheck Hide extensions for known file types; & uncheck Hide protected operating system files. [If you want you can set these things back once you're done.]
2) in Windows Explorer navigate to C:\Users\ [UserName]\ AppData\ Local\ , find IconCache.db, rename it to something like IconCache.d_ or IconCache.old, & restart Windows.
That's the easy part, but sometimes this is a recurring problem, & deleting that file a few times a week, or more, tends to get old, quick. In that case:
1) open Regedit -- go to the Start Menu, & A) click Run, typing regedit into the box & then hitting Enter or clicking OK, or B) type regedit in the Start Menu Search box, then right click regedit.exe & run as admin.
2) navigate in Regedit to HKEY_CURRENT_USER\ Software\ Classes\ Local Settings\ Software\ Microsoft\ Windows\ CurrentVersion\ TrayNotify, right click TrayNotify & export this key to a .reg file just in case -- you can always put things back by double clicking that .reg file or right-clicking it & selecting Merge. Note: to get to that key quicker, when you open Regedit there are 4 major headings in the left pane of Regedit's window -- click on HKEY_CURRENT_USER, go to the Edit menu & select Find, then type TrayNotify in the box, clicking Find.
3) right click & delete the 2 values IconStreams & PastIconsStream. They'll be re-created when you restart win7, though you *may* have to redo or reset any customized tray notification settings.