HP Pavilion zv6000 shutting off or freezing

I’m having a problem with my laptop. It’s either freezing to where the cursor won’t move or it will shut off abruptly (like it has a immediate loss of power even though the battery is attached and it’s plugged in.) I’ve taken it in twice and they aren’t finding the problem. Going to take it in for a third time this week. Any ideas? HP had me run the laptop on Bios and all was fine. I always use it on a hard surface so over-heating doesn’t seem like a issue. I’ve done defrag, disk clean, spyware cleaned and have Trend-Micro anti virus. Anyone else have these issues? The laptop is almost 2 yrs. old.