Mac will start up but wont boot

[Hello??]

Hi guys,
I have a Macbook pro that i bought at the start of last year and have just started having problems with it not turning on. When i push the power button the start up sound happens and then I hold down alt to choose mac HD but after the little wheel spins and eventually a folder with a question mark pops up. I have been reading through these threads and have tried inserting the Mac OS X install disc and trying to repair disk but everytime i do this it saids error can't unmount hard drive. I have also tried just completely erasing my Mac HD but it also it cant do it because it cant unmount HD.

Some help would be appreciated
Cheers

 

[Macman45]

Can you run the AHT? (Apple Hardware Tests) from your installation disks?

http://support.apple.com/kb/HT1509


It sounds like a dead or dying HDD.

 

[Hello??]

Yeah just run it then and it said no problems found

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Is there anyway that I can unmount the hard drives? I don't see what applications would even be running and have been scrolling through forums for a while now and can't find an answer for it?

 

[chown33]

Your hard drive is probably going bad. Or is already bad. This can happen regardless of any SMART status that says its ok.

Another possibility is a bad cable to the hard drive, or a bad connector.

The repair for a bad hard drive is to replace it. Trying to unmount a bad drive in order to reformat it is pointless. If it's not responding properly, it's not going to respond properly to attempts to unmount it.