Shuts down and doesn't start ... sometimes

Question

So ... I've been having this problem for several months. My Macbook will go into what appears to be permanent sleep mode -- in the middle of my using it. I will have to power down by holding down the power button. Then, it won't restart; same thing, almost as if it boots in sleep mode.
If I leave it sitting off long enough (hours), it will turn on again, usually. Sometimes it will work for several days; sometimes only for an additional hour or so.
I have taken it in twice for repair. Both times the Macbook was returned to me with the repair person telling me that all they had to do was let he battery drain and then charge again and it worked fine. Of course, I take the Macbook home and it works for a day -- then, black screen -- and I'm starting all over again.
Does anyone have any suggestions? My Macbook is out of warranty. At this point, I basically need to convince a Mac repair person of the actual cause of the problem, because I need this thing fixed.
I already installed the most recent firmware.
By the way, I've had the logic board and heatsink replaced twice (long before this latest problem happened), I've had the battery replaced and I've had the charging cord replaced because the wire actually burned through the rubber.
Thanks

Answer 1

Many times a laptop overheating is directly related to the cooling of the processor. The main culprit is the fan. The fan sucks in air from the bottom and blows it out the side. It will also suck in hair, dust, and other debris. That stuff often gets trapped by the heat sink and over time builds up in a layer which chokes off the cool air going to the processor making the fan work harder.
Check this out:
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01657439&tmp_track_link=ot_faqs/top_issues/en_u...
What I recommend is getting some canned air and blowing out the vents in the side and bottom of the laptop. If after doing this you still have problems with over-heating, and your laptop is in warranty, you can take your laptop to a HP Authorized Service Center and ask them to clean the fan and heatsink. You can check your warranty here:
http://www13.itrc.hp.com/service/ewarranty/warrantyResults.do?admit=109447627+1286541891570+28353475
If it is out of warranty, consider searching for the maintenance manual for your specific model, in the manual there are schematics for taking apart the laptop. Cleaning the fan is much easier that removing a motherboard, so don't feel to intimidated by the idea. Also you can remove the heatsink and then remove the thermal grease and apply a new layer which also helps alleviate heat related issues.
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