Hi I owned this PBG4 for more than 2 years and everything is good until just now (an hour ago) it crashes I think!!!! I have my Adium stuck and so I force quit with Option+CMD+Esc then the color wheel appear for awhile too and nothing can be click, so I hold the power key and force the system to shut down... Now i try to start up again it won't boot up any more!!! The furtherest is able to see the Apple logo and the spin wheel then shortly it appear with the no entry sign with the spinning wheel going on! I've tried all methods I could online...(PRAM, hold Shift key etc...) Nothing can be done!!!!!! HELP PLS... I've got plenty important data inside and I haven't get a chance to back it up...