dv6-3163cl doesn't start without hard reset

My dv6 laptop won't start without a hard reset (remove the battery, AC connection and hold down power button for 30 seconds), it will then restart, either from the AC alone or the battery.   It does this from both shut down and sleep.  Battery checks out okay, I have reseated the ram, and unpluged and repluged the sata hard drive.  Only other thought is the cmos battery?  Is this a possibility, any other thoughts about this out there? Thanks - Mr.Walt