[PROBLEM] No Boot in AHCI mode (only IDE) w/ SSD Samsung 840 pro, SSD cache malfunction, VGA 740M Error Code 43

Notebook Model: Asus S550CB
**Note: This notebook has by default a Kingston caching SSD 22 GB**

I've swapped the standard Hitachi HDD with a SSD Samsung 840 Pro as stated in the manual with success. I open the BIOS in order to boot from DVD and i noticed the boot options weren't available, but i've managed to boot from the ODD by disabling these parameters in the BIOS options:
-Secure Boot Control
-Fast Boot
and instead by enabling
-CSM and its submenù -PXEOpROM and also by switching to IDE in the SATA control settings. (AHCI was the default).
So I installed succesfully my version of Win 8 on the Samsung SSD. Then i tried to switch back to AHCI in order to get the most from the SSD but no matter which settings i choose the AHCI mode just won't recognize drives and boot: the PC will just boot into the BIOS.
1st weird thing: DEFAULT AHCI mode won't boot anything....neither the original Hitachi HDD....

Then i tried to force the AHCI mode in the registry by settings these parameters to 0 (default 3) (Found this solution on random forums and apparently it worked for everyone but me)
- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es\storahci
"Error Control": DWORD = 0
and
- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es\storahci\StartOverride
"0": DWORD = 0
This method requires to switch to AHCI mode on the very next reboot ..the S.O. should fix itself..but again it just won't boot in AHCI.
So i switched them back to their default values and looked in the Device Manager to check for any errors/conflicts. No errors and HDD, SSD and ODD were working correctly. The Device Manager instead reported an error on the VGA (NVIDIA GeForce 740M). "Windows has stopped this device because it has reported problems. (Code 43)" --> driver/adapter error. I've just installed every piece of driver available in the known universe but the error is still there..i tried with the ones from ASUS Support's page for my model of netbook, the ones from NVIDIA official sites and even the latest beta version (which were the ones i had installed on the HDD before starting this mess).
Last error is a malfunction of the SSD Cache ..ExpressCache is the software which should control it. When i try to check the SSD's status with the command "ECCmd -info" i get this error:
"ExpressCache Driver is not installed.
**ERROR** ECCmd exited with error 0x1 <1>".
(Yes, i did "cd c:\program files\condusiv technologies\expresscache" and then "ECCmd -info" with an elevated command prompt).
At last i tried to install the drivers for it aka IRST x64 (Intel Rapid Storage Technology) from the Asus page of my notebook..but the installer says "Wrong configuration" or something like that.

To recap the errors are:
1- AHCI mode doesn't "see" the drives and doesn't boot, IDE mode with -Secure Boot Control & -Fast Boot disabled and -CSM enabled does boot and does recognize the drives. (again AHCI is set by ASUS..i bought it like so)
2- VGA "Code 43 Error" reported in the Device Manager. Can't fix through driver installation.
3- Standard SSD Cache doesn't work.

*****These errors appear with the original HDD too after the installation of the SSD in the pc*****

I kindly ask for help since i need the ***king pc and I hope someone will be able to help me and/or advice i.e. try to buy anothery mobo and/or vga? just get a new model w/ warranty? yet how to get the ssd working? Please please please..
thanks in advance to anyone who'll answer ..if any

Device Manager Screenshot http://i.imgur.com/XXID875.jpg