This one is pretty common.

by R. Proffitt Moderator - 2/18/13 12:45 PM

In Reply to: HP DM1z netbook won't start by Dcorr83

There is a bug in many that never was cured but the workaround is pretty simple. Remove power, unplug the AC then press and hold the power button for 60 seconds. Slip in the battery (a good one, don't slip in those 15 minute or less batteries) apply AC and try again.

If this fails it's some other hardware issue.
Bob