Grey Screen wont boot up need help to check my hard drive

Several of your answers to questions were very helpful. At first I had White screen, if I let it boot for 5 to 10 minutes I get directory symbol with ?. I P R reset it and got Problem LOG. Localsytem crash log(92), last of many was Thread 5 Exception: EXC_BAD_ACCESS (0x0001). I have tried

restarting from startup disk, OSX 1.4. I got no responce from reboot with D held at start, I was trying to get it to check hardware. I think from the answers I read, I am down to the hard drive, a 298.1 GB WD C WD3200 which Apple replaced when my drive died 2 years ago. Should I check the connectors, can I do a hardware check. When Repair Disk, Disk utility stopped repairing and "Underly task failure on exit. I'm not a tech, just a user trying out your advice, Australia.