CPU idling at 60/max 100, clean system, believe good therm paste

Hi, I have been struggling with BSOD in my HP DV-6 1268nr (specs: Product Specifications - HP Customer Care (United States - English)) for some time now. System is 3 years old; went back to HP after 6 months for new heat sink. Is also idling with CPU temps of 60C and shooting into the 90s if I do just about anything.

Have tried many small random things I read to try (e.g. disabling HD audio), but more recently I reinstalled Windows (no fix), then took apart my laptop (had been avoiding it since I've never taken a laptop apart). Fan and heat vents were pretty clogged, so I fixed that. Also reapplied thermal paste (Arctic Silver 5) to CPU & GPU using the instructions from the Arctic Silver website.

On restart, the PC would hybernate itself after a few minutes. I was guessing overheating, so went back in and took off a bit of the thermal paste (it had squished out the side a bit and too much paste was indicated by the Arctic Silver instructions as a possible culprit in overheating). I also installed CPUID to monitor my temperatures.

I was still having the hybernation issue, so I opened the PC back up. And saw that the fan was not plugged in! (I use a cooling mat so hadn't noticed since I have external fans also making noise). So I plugged the fan back in, and the hibernation problem went away. But according to CPUID my system is running pretty damn hot, even after setting the power settings to power saver. I also had another BSOD while running a Sliderocket slideshow. My temperatures, in celsius, according to CPUID (as of this boot session):

MB: min 55 max 91
CPU: min 52 max 99 (idling at around 60)
GPU: min 50 max 61 (idling at 55)
Assembly/air flow: min 42 max 47

To complicate things, I think this PC has always run hot (see the warranty replacement of the heat sink), as the fan has ALWAYS run really loud and seemed to struggle a lot (as it is now). Is there anything I should try?

Sorry this is such a complicated story, feel free to ask me questions. Thanks for any help.