cc-333 is correct the problem is the bourns filter has gone bad.    its a common problem.

they go bad in a few different ways, causing oddness. i change those... but usually i suggest that if you change one, you should change all 3.  if one is starting to go bad, its probably going to start happening to the other ones as well causing other strange oddness.

(6) If solution (5) doesn't work either, replace the network filter RP2 (Bourns 4120R-601-250/201).
Also see 9. Bright Monitor with neither Arrow Pointer nor Startup

Click to expand...

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html

these filters do go bad on many other mac's as well.