Missing Icon in Notification Area

[Painter7]

A glitch has arisen during boot. Running XP Pro 3, fully patched, the boot process has slowed considerably as if Windows is looking for something missing or some file it needs is damaged. The manifestation of the problem is in the Icon Notification area e.g. containing the clock. Hide inactive icons is not on. Nonetheless several Icons do not now appear. E.g. that for Eset Nod32, for Comodo, for True Crypt etc. Oddly some do appear, as they should, e.g. Spyware Doctor, the network icons, Sandboxie, an HP Printer Icon and EPU-6 Engine. All of the actual programs cited from the antivirus & firewall to the Engine seem to have started ok during boot as evidenced by using task manager and identifying the related processes as being ok and running. The issue is that they do not show in the Icon Notification area. Another anomaly: I looked to ensure that I had not turned on Hide Inactive Icons on the Task Bar and Start Menu Screen. I clicked it out of interest and while scrolling the Customize Screen the icons associated with various programs are wrong.
Thus – Where might I look to identify the problem

[glc]

Try doing a system restore back to a date/time when it was still working properly.