My main PC (Windows XP SP2) behaves itself very well -- apart from when it boots up.
The desktop appears as normal. However, for about 10 - 15 minutes after booting up, there are a lot of things the system won't do. Essentially, system files seem to be locked down. The easiest thing is to give examples:
I cannot install programs (that write to the registry), or indeed edit the registry at all. I cannot use IE, or any program that uses the IE system files, but I can use Firefox. I can't access system management utilities (e.g. if I access Start Menu ->Settings->Network Connections, the menu will freeze on the screen until the system "unlocks").
So generally speaking after booting up I just leave the computer for a quarter of an hour or so. I know when it's ready to use, as my mail checker program bursts into life and all the shortcuts on the desktop "blink".
Obviously I've run plenty of virus/spyware checks. The Event Viewer doesn't seem to offer any obvious clues.
The only other odd system behaviour (not sure if it's a clue) is that, when copying/moving files, the system uses huge amounts of CPU activity, much more than other computers I use. In particular, when receiving files from other machines on my network, the system slows down badly and hits 100pc CPU activity, which is odd. But this happens all the time, so I doubt it is related to my boot up problem.
To be honest I've been putting up with the boot-up glitch for many months because, apart form this, my system is amazingly stable. I can (and do) leave the system running for days without any problem. If I need to reboot, I just leave the computer and have a cup of coffee. So it's really not that big an issue. I'd just like to solve it....any ideas?