Help Alarm clock on HTC desire does not work

[Hadron]

Alarm volume is a separate setting from ring or notification. So I don't doubt you that is a preset on the stock Desire called "Silent" which silences ring and notifications but not alarms. But it doesn't *have* to be like that - it is possible to turn the alarm volume to zero as well. Hence my suggestion was to check that no app was doing that - not selecting a preset mode, but actually muting the alarm.

I know this is possible because I have such things deliberately on mine.