Early 2008 15" Macbook Pro acting very strange

Question

So long story short, I bought a used early 2008 15" Macbook Pro and I keep having issues with it. I replaced the hard drive, replaced the thermal paste (after removing the old paste of course), cleaned her inside and out, updated software, firmware, & reset the pram/smc. None have totally solved the issues. I constantly have files from the hard drive disappear, then reappear whenever they want. The backlighting on the keyboard doesn't want to work if I am doing multiple things like, iTunes, TuneUp, & surfing the net, it just suddenly stops and if I try to activate by using the F6  on the keyboard I get a symbol of a circle with a line through it. The only way to get the keyboard to light up again is to reboot it. The hard drive I replaced with the old one is 500 gigs at 7200, 32mb cache. She also warms up rather quickly even though I used the artic silver thermal paste. I can never seem to get her temp below 45-55 Celsius. I even took apart the tiny internal fans and cleaned them thoroughly. I build desktop systems as well as repair laptops so I do know more than the average user but I am at a total loss here on what else could be the cause of all this strange behavior. I don't know what, if anything the previous owner did with it, which makes it even harder to figure out. Could this be a logic board or power supply issue? There are no other problems with power other then needing to replace the battery, but since it is plugged in everytime I use it, I really don't think this is the cause. Any suggestions are welcomed :-)

Answer 1

check out everyting here
https://discussions.apple.com/docs/DOC-3046
https://discussions.apple.com/docs/DOC-3172
https://discussions.apple.com/community/notebooks/macbook_pro?view=documents