Major difficulties installing Windows 7/8.1

Question

Firstly, I'd like to apologize for my not so perfect English, but nevertheless - here's my cry of help.
Recently, I've had a "pleasure" of messing up my already installed Windows on my iMac (27-inch, Mid 2011) that has been installed for almost 2-3 years and worked in harmony with Mac OS. Back then, I used a DVD disc to install Windows, so I thought it shouldn't be much of a trouble installing it now on OS X Yosemite (boy, was I wrong).
While trying to reinstall Windows for the first time, it couldn't find any drivers on my CD/DVD or USB flash stick, even though my installation DVD was in the optical drive and USB stick with all required drivers was in place. Although, my USB flash drive was formatted FAT32 and after that failed, I've tried formatting it to ExFAT (which both of the options failed). So I thought: "Alright, I'll burn a new DVD with drivers for bootcamp on the DVD itself this time, instead of a flash stick". Same result.
I'm sorry, but after 3 days of failed attempts at installing Windows, I might have forgotten other methods I've tried to continue my installation. So I'm just going to list all things that I've tried failed.
Using bootable USB flash drive with Bootcamp Support Software on it.(EFI boot) (Using Boot Camp Assistant, which wasn't even an option on my iMac, so I had to make some adjustments in terminal and info.plist) *
* After successfully performing this method, I was able to choice on which partition I'd like to install Windows. So I choose the one partition, that Boot Camp Assistant created for me. It declined to continue, because the partition wasn't formatted for Windows OS. After formatting Windows partition, I've stumble upon another error which was something about changing my partition from MBR to GPT. I've googled the solution and that is to access Command Prompt and format partition using "diskpart" utility. I went on selection which disk and which partition I wanted to format(which I checked twice, if not more). After converting the already clean partition to GPT space, so I could continue - for some reason, diskpart utility decided wipe out my whole disk clean(including MacOS). Not knowing that you can restore your OS and all your files using Time Machine, I was terrified. After that, I decided not to install anything anymore, simple because I was tired of infinite reading and researching on how to properly do it.
Using bootable USB flash drive. Only this time, I've made partition as a free space in Disk Utility. *
* This method is actually worked out, though not so well. I was able to install Windows 8.1 this time, but it had no sound. No driver, and not a single solution (regarding tweaking some settings in Device Manager or Sound folder in Control Panel) didn't helped at all. And now, I having trouble switching from MacOS to WindowsOS, because for some reason Windows partition is labeled as "EFI boot" and it is asking me to insert a bootable USB installation flash drive to continue.
I'm pretty sure, methods mentioned above is not all of the methods, that I've tried. But I think, at this point, I've tried everything there is to try in order to properly install Windows.
My main point is that I've decided to test my optical drive both on Mac and Windows and see, how it is able to read information from DVD disc. It was loading files, that was on DVD, very very slowly. Sometimes not even loading them all. It just went on spinning in optical drive, making humming noises and reading sounds. Now, when I think I've understood what was the main problem of failed installation using DVD disc, my questions are:
What can I do at this point in order to install Windows properly?
Is the optical drive really the main reason, that Windows couldn't locate some drivers? Because I remember my first attempt at installing with DVD, I've made it past the partition selection, but my installation stopped at 1-2% giving me the error)
How can I fix an optical drive?
Is it even possible to fix?
Oh, I've also trying to burn a Windows ISO onto my DVD using iMac, which gave me a Medium Write Error at the end of the process.
My apologies for the wall of text, but I don't know what to do at this point. I'm leaving outside of US, so there is no official Apple building in which I could ask for replacement or asking to repair my optical drive. I'm pretty sure my warranty is expired by now too.
I will answer any question, but please help me fix this problem that I've created myself... Thank you.

Answer 1

I know this is a stretch... but have you tried using a retail Windows disc instead of your own homegrown copy?
Let me be frank, I've never had any retail Windows disc (both physical and ISO versions) in my entire experience with computers. This one disc, that I used to install Windows with 3 years ago worked perfectly back then. (without me even using any USB flash with drivers on it) I had second disc for it with drivers on it and as much as I could remember, I've never ejected Windows disc during the installation, so that I could insert the second disc and it could find "device drivers" to continue. (yet again, I might be completely wrong here). But the idea of ejecting the Windows DVD during this "device drivers" error was terrifying to me. Even if it told me, that "ejecting the Windows disc at this point is safe". I don't even know how to eject the disc during this error manually from iMac. Please, if you have any suggestions and really think that I should eject the DVD during this error - I will do it, if you tell me how. Come to think of it, why it couldn't find any drivers on USB back then is beyond me.
My suggestion is to verify the ISO and DVD both using M$ FCIV tool. http://support.microsoft.com/kb/841290
I will try doing so, thank you.
If the ISO is valid and BCA will let you create a USB (without modifying BC Info.plist), it is a much safer and supported route.
No, I don't have any option of creating a bootable USB in BCA, I had to modify info.plist myself back when I try booting from USB flash.