Question : Problem: iMac G5 Screen goes black suddenly  in the middle of simple task

The internal fan? starts working harder and the mouse pointer freezes and the screen of my iMac G5 goes black suddenly while I am watching a YouTube video or doing something simple such as clicking "Ask a new question" on Expert-Exchange page using FireFox. So I am writing this in Safari. But when I watch a video on the Internet using Safari, this problem often happens too.

I have had this problem for the last few months and it has been getting serious. When the screen goes black, hitting an arrow key recovers the screen back but unless I move out of the Internet page or quit any program that caused the problem, the screen keeps turing black and finally the computer freezes. I experience this very often a day. Recently I purchased a 3D software that uses Projector and every time I try to use it for a couple of minutes, the screen freezes and I cannot use the program.

I have not installed any anti-virus program and I rarely turn off the computer unless I go out of town.

The following are things I tried (I got the ideas through Expert Exchange or some other site) but so far nothing has cleared this problem although I do not know what I am doing entirely.

1. I checked the serial number and  EMC number of my iMac G5 and both  are not included in  "iMac G5 Repair Extension Program for Power Supply Issues" and "iMac G5 Repair Extension Program for Video and Power Issues."

2. Resetting PRAM and NVRAM

3. Running Disk Utility's Repair Disk Permissions

4. I checked Activity Monitor but tasks causing the problem did not use much CPU.

I did not add any RAM.

Is it time to buy a new computer? Should I bring it to the Apple store? My warranty ran out of it long time ago.  It seems my G5 is still working when I do not do something that makes the fan working harder. I would really appreciate any advice you have!  

Answer : Problem: iMac G5 Screen goes black suddenly  in the middle of simple task

strung,
Thank you! I followed your instructions and made sure the S.M.A.R.T. status was  as "verified." When I tried to run the  hardware diagnostic CD. my computer shut down. I tried it again but again the same thing happened.

hobowankenobi.
Thank you! I wanted to follow your instructions. Then I tried to open my Mac.  Then I found one thing.

The vent of my Mac was clogged and I cleared the clog by a vacuum cleaner. Since then, I have not had any problem.  

But I really liked to get advice from experts, such as strung and hobowankenobi and I decided to subscribe to  the service  for a while. Thank you again!