For the longest while now, I have been living with my laptop deciding to hide some of my Systray icons (the ones on the right of your Start/Task bar). The only way that I knew of to get them back was to kill explorer.exe and then re-enable it via Task Manager.

Today I did a bit of a Google and discovered that this issue actually plagues many users! It seems that almost always there is a link to UPnP services.

For a vast array of possible fixes and workarounds, check this page - Systray Icons Missing

For an alternative, slightly easier but substantially less comphrensive page, check here.

For me, the solution was the 'Otumi Workaround'. Basically, this involves going to 'My Network Places' and clicking the option 'Hide UPnP Icons' (or something similar). One restart later and the missing icons returned!