Boots, Fan runs fast, then black screen <<SOLVED>>
My computer starts up, all 4 LED lights are on solid green. After about 5 minutes the fan speed starts noticeably increasing. 5-10 minutes later the screen goes black and the #4 LED goes off, leaving LED's 1 through 3 solid green. The iMac doesn't shut down and fan continues to run until I hold power button down to shut it down.
If I restart immediately, the screen lights up & the same situation happens. If I wait for a while to reboot, it seems to cool down & the fan speed is normal for about 5 minutes and the same symptoms repeat.
I have: held power switch down with power disconnected for 10 seconds, reset PRAM, installed a new HDD & tried fresh install of Mountain Lion (only because had to get data off previous one).
Any help greatly appreciated!
iMac 24" 2.8 GHz EMC No. 2134
<<Answer to question, Nothing happened before this starting iMac was working fine & no electrical surge issues >>
**Problem Solved, I decided to take my iMac in to local repair shop, the replaced the video card for $250. Unfortunately they didn't Zap the PRAM so I kept getting error messages when trying to install Lion or Mountain Lion, but after zapping PRAM work great. Thanks very much for the replies !!!