My computer would randomly shutdown. Not sure if it was power supply, ram, or temperature issues.
For the ram, I realized you could download memtest for free and run it in Terminal to see if it was the problem. My Ram was still good. So I didn't change them out.
Unfortunately, there was no direct guide for the power supply, but I based it on a 20" iMac Intel EMC2266 guide and it was nearly the same. Screws were little different all over, so I used my magnetic project mat to keep track of where they all belong and it was very handy for sure. The toolkit had all the random bits which are not usually found at hardware stores. I thought the alligator clip for the antistatic band was fairly weak and it couldn't clip anywhere without falling off when I moved. Also the handle for holding the bit is mostly metal and was hard to turn some very tight screws alone. Other than that, the instructions and change out was smooth with the right tools. I'm sure next time, I would be able to do it again without any instruction.
Get one of those compressed air cans to blow out dust or carefully vacuum. Build up of air garbage over the years can lead to failures. Also download and run memtest before buying RAM.