Extremely Slow Start-Up, Slow to Start Typing, What is Wrong?

Hello,

I am trying to fix a MacBook Pro, but have not before encountered such symptoms.

---- What I saw and tried, chronologically:

- When it came, the laptop would get stuck at the spinning wheel.

- I removed the HDD, tried to repair it through USB connection on my own Mac, Disk Utility said it was OK;

- I tried to boot on the "bad" machine and "bad" HDD again, but through USB, got stuck at the spinning wheel;

- Took it apart: no signs of water damage or past repair; replaced the HDD cable for good measure => the laptop started getting to the prompt at the 94th second;

- Trackpad works at this point, I could move the mouse around the screen, but when I clicked on "restart" or "shut down" I got nothing;

- I tried to type use name and password, but the cursor remained stuck on user name, didn't move or register anything;

- After a while (2+ minutes, can't say) the letters I had typed before now appeared in the prompt with a delay. I logged in, and the computer behaved normally;

- I restarted it, and got the same issue again;

- Tried 1*4GB RAM 1067 in 1st then 2nd slot. Did not get to the prompt or hardly.

- I put back the 2*2GB, would still get screen color change at 94 seconds, but the prompt for user/password wouldn't appear. Once, I got distracted and when I looked back, it was back to the spinning wheel after it had "changed color.

Anyone can suggest what the problem is or how to trouble shoot it?

Thanks!

Additional info: MacBookPro7,2 / 2.4GHz Core 2 Duo / 2*2GB RAM / Attached: thermal pic of the board, seems OK I believe (outside/around the red area, temp is 45 deg. C)