27" iMac Mountain Lion won't boot (Black screen) after switching to bootcamp

Hi,
I've been running Windows 7 in Boot Camp on Mountain Lion on my 1 month old 27" iMac without any problems. Tonight after I switched the startup partition to be boot camp the machine won't boot. I get the startup sound and the disks spin up, but the system just sits there with a Black Screen. There is no disk activity other than them spinning up.
I've tried starting the machine while holding the option key and also command-r, but nothing is happening. I have the feeling that the bluetooth keyboard has not had the chance to connect to the system before it is hanging.
I tried inserting a Lion OS DVD, thinking that it would at least complain and give me an option to boot back in to Mountain Lion. You can hear the DVD spin up and then go idle.
Any suggestions on how I can recover the situation?
Thanks in advance
Mick

The RAM mismatch might be the problem fix that.
Also backup/data recover naturally, assume TimeMacine or bootable clone is corrupted and backup only files to a storage drive
Most commonly used backup methods
Install OS X on a external drive and boot from it.
Create a data recovery/undelete external boot drive
Use Disk Utility on the booted clone to Erase with middle selection (Zero) the ENTIRE internal hard drive
Use Carbon Copy Cloner to reverse clone the clone onto the internal, copies the Recovery HD too.
That should fix it, or else the drive or another hardware issue
..Step by Step to fix your Mac
Install/upgrade RAM or storage drive in Mac's

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27" iMac Mountain Lion won't boot (Black screen) after switching to bootcamp

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