New HDD / Win2K Pro Hiccup at Power-up

I have a three-year-old Dell Latitude CiPR400GT and replaced the HDD with a new 20GB IBM drive. I installed Win2K (SP1) and I get the following problem and symptom consistently.

At power-up the Windows splash screen comes up and when the progressmeter reaches the halfway point the computer goes to sleep. The only recovery is to hold the power button to power down then press it again to turn on. It then usually starts up more or less normally though occasionally this must be repeated.

Thesymptom that appears tenuously related is that although I keep the speaker muted in the control panel, each time I power up I have to mute it again.

Strange twist: from time to time I shut down the computer, take it home and turn it on there and the start-up is normal. i.e. no standby and no unmuted speaker.

Ideas, please!