Prior to this, the computer was on as normal, for internet browsing and no intensive tasks for several hours. I turned it off for approx 20 minutes, then this happened. I do not know what the CPU temperature was at any time, but about 2 hours after this problem surfaced, I opened up the case and heatsink to see if anything is loose. Nothing is loose and the CPU temperature is cool to touch. No idea if it was too hot earlier.
Also, when computer was fine, when I remove and insert the cable, heatsink fan will blow for a few seconds even with computer off (but power supply on).
Now it doesn't respond when cable is removed and inserted.
Anyone has any tips/idea/experience which component may be broken? Is there some sort of temperature sensor which may have broke, which causes the heatsink fan to superspeed and the boot system to automatically not start? Or perhaps did the CPU died?? How easy does the CPU die if it just overheats for a few minutes?
Try resetting your bios back to factory settings. If you don't have a reset button then unplug the computer from the wall, hold the power button down for a couple of seconds, remove the cmos battery for a couple of seconds and repeat the power button trick, (clears any residual energy), put the battery back in, plug it up and turn it on. Sometimes they mess up.
If that don't work follow the link under my cpu=z banner and do the checklist.
I had a motherboard do that one time and it got thrown away.
I had a similar problem earlier, several attempts at fixing eventually fixed the problem (after adding a new video card) but I was never sure if the video card was the problem. Then the problem occurred again (after a few months). So I was getting ready to pitch the computer when I read about a problem with the heat sink connection (which makes sense why the fan goes to jet engine speed). Haven't had a chance to try it out yet, but will go home and see if I can get it to work. Read the details in this blog https://binglongx.wordpress.com/2010/12/12/dell-dimensi...
See if this works for you. I am assuming that when I was messing around with all the parts on the board, the heat sink got pushed to the back of the case, and the boot problem went away for a while.
And pick up some rubber bands if you don't have any at home. I am keeping my fingers crossed that this will work for me.