My computer wouldn't stay on. Sometimes it wouldn't turn on at all. Sometimes it would turn on then immediately shut down. Sometimes it got to the desktop and then it would shut down. I left the computer in storage until recently when I really needed to use the recording software.
I have an iMac "Core i5" 2.5 21.5 inch (Mid-2011) 2.5 GHz Core i5 (I5-2400S) EMC no. 2428, Model - A1311. The repair went easier than planned. I had no idea what was wrong. I initially suspected it was the power supply, so I ended up on this website looking at the power supply replacement guide. I am hurting for money, so I thought it best to just look inside and see what I can figure out, so I bought the heavy-duty suction cups (pair) and TR10 screw driver. I actually used this video to learn how to get into the iMac: https://www.youtube.com/watch?v=RmLLzkg3...
After opening it up, I realized there was a bunch of dust, as shown in the pictures. I powered it on while it was open and it seemed to stay on. I didn't have any canned air so I just put it back together and now it works fine! I'm assuming it was overheating from the dust buildup and I dislodged some when opening it up. I will get some air and go back in to clean it out.
Do stuff for yourself, even if you never have before, just keep a positive attitude. This was my first computer repair and the internet had a wealth of information. I saved so much time and money! IFIXIT had the items I needed to do it. I chose the standard shipping, though I wanted the two day (just didn't want to pay the extra $), and it came just as fast! Really pleased, I see myself using this site again. It was very satisfying opening it up, and may have sparked an interest to get into computer repair. ^_^