Started auto shutting down and/or restarting and cursor started freezing. Once a kernel trap message showed upon start up at grey screen / apple phase. Once the start up chime kept chiming over and over. Tried PRAM & SMC resets. Powered up after one PRAM attempt and lasted 20 minutes before cursor froze. No response to further resets. SIL comes on fades off for a sec before coming back on. One faint, barely audible noise from hard disk, no other sound or action. Screen stays dark. Manual shut down turns SIL off. No access to SuperDrive and start up disc ATM so no hardware test for now. Any help would be appreciated. Thanks!