(I dont have much time to search 50+ threads to see if this has already been posted)
I had the problem with my alarm not going off while my device was in sleep mode and plugged into a power source. I came across a possible remedy (not a work around. :P )
The remedy presented itself when I needed to review a document for work at 7am before I left for the office:
I set my active-sync to auto pull from an Exchange server at 7am.
I also set a meeting maker via my calendar for 7am.
While plugged in to a power source, and in sleep mode, my device wakes up to issue my meeting reminder, and at 7am it pull from Exchange and notifies me of new mail. It also issues my 7am alarm as well. (All while still plugged into a power source.)
Since then, I have moved my active sync to start at 8am, and have no 7am meetings. But sure enough, my 7am alarm now pulls my device out of sleep when plugged in and works just fine.
I sure as hell have no plans to hard-reset and retest
-TheRealJobe