CHECK 1:
Remove power connection, remove battery, replace battery and try again. Might fix your problem by now.
IF NOT FIXED YET:
If it tries to turn on but keeps cycling in 3-10 second reboot intervals, turns on for 3 seconds then reboots and does it over and over again. 'CHECK 1' again then. 'CHECK 2'.
CHECK 2:
As you hit the power button, after having done 'CHECK 1', hit escape a couple times this should force a boot under any condition.