i have a hp compaq 8510p when it is on the desktop the fan comes on loud then it shuts down

my hp8510p is running win 7 ultimate with 4 gigs of ram. it was running good for years and now when I boot up and on desktop the fan comes on loud then it shuts it self down. I am running the vision diagnostic hopefully that will tell me exactly what is going on with it. I have been pricing mother boards and cpu the cool thing is they are affordable. I think its a good laptop does have most the latest features I might go the route of updating the board and cpu if that what it takes.
how do I find out what the highest board and cpu I can put in the shell? I shopped around for ram a few years back and was surprised to find out the older ram is more expensive than the newer ram lol. anyway any feed back on what boards and cpu I can put in there and what might be causing the high fan then shut down issue?

 

Open the couple screws marked with keyboard logo under the laptop. Then open the laptop, flip those 3 or 4 clips on the keyboard and lift it up. Then proceed to remove the fan and clean out the collected dust on the heatsink.

See if that helps?