Acer Veriton M460 Quad won't start after running Vista Scheduler

I have a new Acer Veriton M460 Core2 Quad PC running Vista Business. Something weird is happening that seem to be related to the Vista Task Scheduler.

I have a complex chain of actions that start from one action. The chain is: run software to download .html files, run Microsoft software, run DOS batch files and DOS executables.

It works fine if I start it from the desktop and if I start it using Task Scheduler.

However, if I used Task Scheduler, the next time I boot up the PC it freezes at the Acer pre-Windows boot screen. Even the set up keys mentioned on that screen don't work, e.g. "press F12 to choose a start up mode". I have to pull out the power plug.

When I plug the power back in, even after quite some time, the PC proceeds with the boot up successfully through to Windows without me having pressed the Power On button on the computer.

So the bottom line is that if I use the Scheduler, my PC won't start the next time I go to use it.

There was an event that may have some relevance or could be coincidence: about a week ago after I first scheduled the task I came back to my PC, which had run my scheduled task unattended after waking itself from Sleep Mode. I found it showing not Windows but the PC boot options menu. I pressed the highlighted option, which I think was Normal. This hasn't happened since but could be related.

Incidentally, my PC was supplied with Sleep Mode set to start after 20 minutes plus there is a screen saver. But neither was going when I last used the scheduler for my task.

Any ideas?