Was on the internet Friday when suddenly the screen went black and system spontaneously rebooted. Came up to BSD with "windows has been stopped to prevent damage...", I hit the reset button and it did the same thing. Rebooted a third time and windows loaded, normally at first - logon screen, windows start sound, wallpaper appears - but neither the task bar nor any icons appeared, though the cursor was there and moved normally. Hit CNTRL+ALT+DEL and got a system beep and the message window: "Task Manager has been disabled by your administrator". I AM the administrator (no one else uses this computer) and I didn't disable anything! Tried CNTRL+ESC ...nothing. Tried the windows key ...nothing. Right click on desktop ...nothing. Reboot again (reset button) - same thing. Reboot - safe mode, no difference except now have "safe mode" in each corner.
Reboot - "last known good..." - same thing except now have have message about "16bit subsystem" pop up when windows starts (this was leftover from "uninstalling" Norton, don't recall how I got rid of it before).
Went into BIOS, changed first boot device to CD, spent half an hour finding CD, restsrt - boot from CD. System starts loading files from CD then stops with message:
File NTFS.sys caused an unexpected error (32768) at line 5091 in D:\xpsprtm\base\boot\setup\setup.c.
Press any key to continue. (I hit spacebar)
Setup failed. Press any key to restart your computer.
System reboots and repeats this procedure.
(Researched this error message online. Seems it is a well known XP install error, though the offending file may be different. One source mentioned that the 32768 was not an error code but referred to 32meg memory, though they didn't elaborate on the significance of this. There was no consensus on a solution, seems people had success with: keep rebooting and the installer went a bit farther each time til it finished; reseat the ram; replace the HD [negates the idea of the repair install]; use a different CD; clean dust from the fans; ...you get the idea.)
Reboot from HD and have same problem as before except now no wallpaper. Shutting down the system (just hitting the power switch rather than holding it down for power off) gets me the normal blue windows screen - "saving your settings", "shutting down" - and my windows exit sound; so, admitting my limited knowledge of the workings of windows, I think XP is actually running normally but that something - virus? malware? - from the internet has hijacked my admin rights, hidden the icons and task bar, and disabled task manager.
But what to do about it?
BTW - at each stage of these proceedings I also tried booting to "safe mode with command prompt". Would get a black screen with 'safe mode' in each corner and my cursor, nothing else. After a couple of seconds it would continue loading windows til it got to the logon screen, before I could even click on 'administrator' the system would reboot.