Try reinserting the battery, press the PMU/CUDA button once for 1 second. Next, turn on the blue iMac and immediately press and hold down Apple (CMD) + Option + Letter P + Letter R. You'll hear the startup chime for 3 chimes. Then, immediately press and hold Apple (CMD) + Option + Letter O + Letter F. This will put the machine into "Open Firmware" mode.
Enter the following:
reset-nvram (hit Return)
set-nvram (hit Return)
reset-all (hit Return)
The iMac will reset and you should hear the startup chime one more time.
If this doesn't work, then it could be a problem with the PAV board, logic board or bad RAM. Try a different RAM to see if things improve, first. If not, try installing an identical logic board from a spare machine. If you get the same results, it's most likely the PAV board.
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