I am wondering whether this has anything to do with a recent update to Adwatch. I have been running it for a long time, but recently when the computer starts (XP home, 3GHz 2GB RAM Dell Dimension 5000) Adwatch comes up with a "cannot start" warning and then either no other startup programs load, or if they do then their icons do not appear on the taskbar.
One the boot is complete, you can manually start Adwatch and it seems to run OK. You can also manually start the virus checker (in my case AVG free) and that seems to run fine. But no other icons like Volume Controls etc appear in the bottom right.
Once the whole boot process went through OK, but the last time I rebooted, I disabled Adwatch and the boot process completed. I then started Adwatch manually. I don't know whether this was another coincidence, but I suspect not. It seems Adwatch was preventing legitimate startup programs running.
Whether or not the problem occurs, my PC runs fine and is well maintained regularly. No sign of malware or virus. Just a nuisance when the problem occurs.