Windows 7: Need help/Unable to install Windows 7 64bit in Sony Vaio Laptop

Hi all, I have a brand new Sony S Series 15 SVS151290X that I recently bought and it came with Windows 8. I removed the internal HDD and replaced it with a fresh Samsung Series 830 256Gb SSD. The SSD is recognized as it show in BIOS. I'd like to install Windows 7 Ultimate 64bit onto it. I have an ISO image of the Windows installation DVD disk and created a bootable USB installation flash drive. I followed the instructions to modify it so that the UEFI Bios will recognize it. I alsotried installing it directly from the Windows installation DVD (the laptop also has a DVD drive). In both cases I'm unable to install Windows, a message shows NO Operating system found. I tried changing the UEFI boot option in BIOS to "LEGACY" and the installation will proceed but it will install Windows 7 32 bit and not 64 bit. I spent hours making all kinds of mods to the USB stick without success. I'd appreciate any suggestions. Thanks.

Unplug all other HD's and peripherals, if you want to install in UEFI mode follow Downgrade Windows 8 to Windows 7.

If not, boot into BIOS setup to enable Legacy BIOS if present. Next check BIOS Boot order for an EFI Boot Disk and if present remove it, set DVD drive first to boot, HD second. Then set SATA controller to AHCI. Save changes and Exit.

Then boot into installer DVD or flash stick burned or written using tool and latest ISO for your licensed OS version here.

At first installer screen Press Shift + F10 to open a Command Box, type:

DISKPART
LIST DISK
SELECT DISK 0 (after confirming Windows 7 target HD #)
CLEAN
CREATE PARTITION PRIMARY SIZE=102400 (for 100gb partition, adjust as desired)
FORMAT FS=NTFS LABEL="WINDOWS 7"
ACTIVE
EXIT
EXIT

Next click Install Now to Clean Install Windows 7 to the partition you created. If it fails then report back at which step and the verbatim error message.

In addition read over these steps to understand the tools and methods which work best to get and maintain a perfect Clean Reinstall - Factory OEM Windows 7. The steps are the same for retail.

Thanks for the steps you outlined, I'm in the process of trying the Downgrade option. In the meantime, I was able to boot from the Vaio Rescue USB drive I created using the Vaio Care software to clone the Windows 8 installation from the original HDD (a mechanical drive) to the Samsung SSD. When I go to Computer Management in Win8 I see the SSD with 5 partitions:
- OEM Partition (260MB)
- Recovery Partition (1.44GB)
- EFI System Partition (260MB)
- Recovery Partition (37.29GB)
- Primary partition (160.12GB)
These add to a total of 238.35GB, but the Samsung SSD is a 256GB HD. What happened to the remaining 17.65GB?

UPDATE:
Ok, so I first tried the Downgrade option without success. I followed the steps outlined here. I disabled Secure Boot from the BIOS so step 2 showed FALSE and booted the laptop from the DVD drive with the Windows 7 installation disk inside. It showed "No OS present". Maybe I should create a custom installation DVD to make it UEFI-compatible?
I then proceeded to try your suggested 2nd method. I enabled LEGACY in BIOS (disabled UEFI). Then set boot order to Optical Drive first and HD second. There is no option to set SATA controller to AHCI in BIOS. I then saved and booted from DVD and completed successfully the Command Box steps. I then continued with Windows 7 installation and the process completed successfully, it now shows 64 bit!. However, if I set the Boot menu in BIOS back to UEFI (instead of LEGACY), it will not boot (the screen displays "No OS present"). So I'm forced to use this Windows 7 installation in LEGACY mode. Will this impact the system performance as opposed to using UEFI? If so, should I keep trying making Windows 7 usable in UEFI mode? I won't install updated drivers+programs/data if LEGACY means some sort of handicap as opposed to UEFI. Thanks again

Why would you expect it to run in EFI mode when you chose the option to install normally without EFI enabled?

I wouldn't have given you the choice if there is any drawback to installing normally to an MBR disk.

Read more about it here: Technical Note: UEFI BIOS vs. Legacy BIOS - YouTube
The 30-year-long Reign of BIOS is Over: Why UEFI W... - Input Output

Well, from what I read EFI is newer and has some advantages over Legacy, that's why I thought that being able to run the OS with the BIOS set to UEFI was better. However I'll keep the current installation with Legacy as you suggest, it also eliminates the troublesome UEFI installation steps (somehow Sony made the BIOS firmware very restrictive to be able to install an OS with UEFI). So thanks for your help, your advice was the only one that solved this issue.
Two final questions:
- Should I set "Secure Boot" enabled or disabled in BIOS? (I tested both and they are compatible)
- The SSD is 256GB but the OS uses 238GB, what about the remaining 18GB?

I don't think you'll be able to run Secure Boot with Windows 7. Read this for more: MS new "Secure Boot" locked BIOS arrives

it's common for partitioning to take up several gb although there may be more overhead if you imaged the preinstall with all of it's corrupting bloatware which throttles Windows 7. Most tech enthusiasts will not run the factory preinstall but instead Clean Reinstall - Factory OEM Windows 7.

Since space is often limited on an SSD it may be even more compelling ultimately to do a Clean Reinstall sticking with the steps that assure getting and keeping it perfect.

Other Best Practices for SSD's recommended here are to install programs and keep paging file on the SSD for best performance, then if space gets tight you can trim the paging file, even turn off Hibernate - both of which use an amount equal to your RAM gb. But you have a big enough SSD to be able to keep those modern features intact most likely.

User folders are normally the first to be offloaded and can be copied to a HDD and linked back using Library - Include a Folder - Windows 7 Forums.

Thanks for those tips