Is the "flashing" an indication that the computer is "sleeping" ? If so, one "tap" of the on/off button might end the "sleep".
Failing that, hold down the on/off button for 30 seconds, until the computer totally powers-off. Then, power-on, and see if it starts normally.
Failing that, disconnect the AC power adapter, and remove the battery. Then, hold down the on/off button for 5 seconds. Reconnect the battery, and the AC adapter, and see if it restarts properly.