If the driver wouldn't install when the Device Manager showed the Standard VGA then either the driver wasn't modded properly or you didn't disable driver signature enforcement right before trying to install the driver. First thing to do though is work out the cmos error. If you replaced the old battery with a correct new one then hopefully the BIOS reset will work. Did you try jumping the cmos pins with all the power removed? After doing this you will get a 5 beep error again but holding the power button down and doing a hard shutdown and then powering on again usually clears it up. If you're still getting the error after this then the new battery is bad or there's an issue on the board. If you can get the error fixed then the rest should be pretty easy. If you go into the Device Manager just see what is listed under Display Adapters. If you just see the Intel 3000 graphics then you're on iGFX mode and if you see the two 780M's then they will be listed as Standard VGA or Basic Microsoft Display Adapters. If you only see the Intel 3000 then press Function - F7 to swap GFX modes. If nothing happens then you'll need to install the Alienware OSD driver and try again. [URL] Once it reboots then check again and you should see the 780M's. Now you can restart again with Disable Driver Signature Enforcement and install the modified driver. If it doesn't install then the driver isn't modded correctly and I can walk you through fixing it.  There is sometimes a conflict with the HD Audio and the 780M on the M18x R1 and M17x R3 and the unlocked BIOS is required so you can disable it before installing the cards. Some people don't have this issue though.  You can't have switchable graphics with SLI, it doesn't work in these dual GPU laptops. By Switchable Graphics, I'm referring to Optimus which switches it 'on-the-fly' rather than having to use Function F7. The unlocked BIOS will open up the option though and it will work if you only want to run a single 780M. I had to use SG mode with my GTX 1070 in my R2 since the 10 series cards won't work in PEG mode with an LVDS display. 
I have a 2012 M18x R1 that I just got home from having the dual nvidia 560m cards replaced with dual 780m. Here’s where it gets weird. My system sees both cards, but only as standard vga. It does not see my integrated graphics card (not even in bios), but it’s using it to display everything because the new cards aren’t installed. Believe me, I’m ticked at the so called professionals who won’t stand behind their own work. I digress. I pulled the cmos battery in an effort to clear everything, but after I reinstalled it, I got the 5 beep error. No matter what I did to reseat it, I still kept getting the beeps, so I replaced the cmos battery. You guessed it, it’s still beeping. Is there a trick I’m missing? I’ve tried pulling the battery and cmos, pressing fn and power and instead of booting, it just keeps beeping. help!
M18x R1, cmos/graphics cards