Windows Fails to start, Start up repair does not launch.

I have been trying to pinpoint this problem for a little shy of a week now. I have a custom built desktop which was running windows 7 Ultimate when it started to have troubles shutting down and booting up. It would fail to shut down and the windows start up would either get stuck for awhile(on the screen that is showing the logo) or it would not start up at all. Hoping that it would solve the problem I reinstalled windows and am now running windows 7 Professional but the problem is still not fixed, It still gets stuck on the start up Just wondering if anyone could help me find the cause of this problem as it is very frustrating. My computer specs are: EVGA 123-YW-E175-A1 LGA 775 NVIDIA nForce 750i SLI FTW ATX Intel Motherboard, Intel Core 2 Quad Q6600 Kentsfield 2.4GHz LGA 775 Quad-Core Processor, EVGA GeForce 9800 GTX+ Graphics card, Rosewill RX630-S-B 630W PFC.

Any help would be great. To add, it will also not start in safe mode and the cd/dvd drive does not always read discs, this leads me to believe it is a motherboard problem.

You can also use this excellent tutorial: Troubleshooting Windows 7 Failure to Boot

So I was able to start windows once(it happens to be able to start up random times when I turn it on) and I ran the CPU stress test, GPU stress test and the Prime95 Blend tests they all passed fine. I try to run the memory diagnostic and the HDD diagnostic but my computer will not boot form the cd it stays on the boot screen saying Boot from CD: but does not boot from the cd. I know I burnt the Image on the disk right and I already tried unplugging and plugging back in the sata cable connecting the cd/dvd drive to the mobo. What should be my next step being that I can't get my computer to boot the diagnostics.

It could be a bad burn so you could try burning the Windows 7 ISO to another DVD.

If you can't get the DVD to boot you might want to consider create a bootable USB pen drive, as explained in this tutorial.

USB Windows 7 Installation Key Drive - Create

I burnt new cd's for the ram and hd diagnostic tests and booted them up. The memory diagnostic failed right away so I reseated the ram and ran it again. It went through 3 passes with no errors then I ran it again and it went through 7 passes with no errors. The hd diagnostic test showed an update for the firmware was recommended so I proceeded to do that. After both of those I was able to boot up no problem. I have rebooted a couple of times to see if it is fixed and so far it has been successful so thanks everyone for all the help!

That is good news then.

Thanks for the update.

If you're happy perhaps you'd care to mark the thread as solved. :)