Is it plugged in?Have you tried turning it off and on again? If the error persists,post error message.
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There may be a problem with the RAM, or you may not have enough RAM on your computer. Look at this troubleshooting page for more information: [https://www.ifixit.com/Wiki/HP_Compaq_6910p_Troubleshooting|HP Compaq 6910p Troubleshooting Page]