OK I've looked through your motherboard manual and I'll copy/paste the relevant parts with some extra explanation following each.
"Chapter 2 BIOS Setup
To access the BIOS Setup program, press the <Delete> key during the POST when the power is turned on."
You've said that the machine boots too fast, but try having your finger on the Delete key ready to press it the same time you push your power button. If you still have no joy bringing up the BIOS setup screen skip down to section 2-4 BIOS Features.
"2-1 Startup Screen
There are three different BIOS modes as follows and you can use the <F2> key to switch between these modes. The
Startup Guide screen (default) simplifies conventional complicated BIOS setup menus and presents only the most
frequently used options in the easy-to-use interface. It helps first-time users to perform basic system setups more
quickly and easily. The ST Mode (for the GA-Z97-HD3 only) provides a fancy and user-friendly BIOS environment
where users can easily point and click through various settings and make adjustments for optimum performance. Classic
Setup is the conventional BIOS Setup interface where you can press the arrow keys on your keyboard to move among
the items and press <Enter> to accept or enter a sub-menu. Or you can use your mouse to select the item you want."
Once you have the initial BIOS setup screen displayed I'm guessing you'll be presented with the Startup Guide screen. Unfortunately they don't indicate which BIOS options are presented in that mode, so I don't know if the option to enable/disable the Intel Processor Graphics will be available. You could browse through that mode looking for it or hit F2 to bring up Classic Setup mode (it will take either one or two presses of F2, depending on whether your motherboard is the Z97 model or H97 model ... my guess is it's the H97 and the Classic mode will only take one press of F2 as ST mode is only available on the Z97 model).
Once in Classic mode you'll use your keyboard arrow keys to navigate through the various menus and options. Sometimes you'll need to use the left or right arrow keys to move the highlight onto what you want, other times you'll use the up and down arrow keys to navigate. At this point you can't break anything ... but pay close attention that as you're navigating that none of the values shown in any of the options changes (shouldn't as you'll need to hit Enter after highlighting an option to change it). It says you can use your mouse to select while in that mode, but I've not used that particular motherboard/BIOS combination and can't say for certain how that works.
If you've managed to get this far without resorting to my suggestions in section 2-4 then you can skip everything in that section and move to section 2-5.
"2-4 BIOS Features
Fast Boot
Enables or disables Fast Boot to shorten the OS boot process. Ultra Fast provides the fastest bootup
speed. (Default: Disabled)
Next Boot After AC Power Loss
Normal Boot Enables normal bootup upon the return of the AC power. (Default)
Fast Boot Keeps the Fast Boot settings upon the return of the AC power.
This item is configurable only when Fast Boot is set to Enabled or Ultra Fast."
These next two items are not exactly one after another in the manual, but both are in that section if you're following along in your manual as well as reading here.
What you've told me leads me to think that Fast Boot is enabled (first of the two things here), even though it's not the default option. If you've managed to get to the BIOS setup screens then we can leave this alone as you've obviously learned how to be faster than Fast Boot (or Ultra Fast). If you've been unsuccessful getting to the BIOS setup screen then this is something we'll need to change back after we're all done (optional).
So if you've had no joy getting to the BIOS setup screen by pressing Delete at bootup we're going to see if they've left the Next Boot After Power Loss option at default. If it has been left at default the BIOS should automatically disable Fast Boot when you're computer losses power while running. If you can manage to get to the BIOS setup screen without using this trick it's the best way, so I'd advise trying the Delete key method a bunch of times (even holding down Delete before you hit the power button) before you try this. What you'll do to use the power loss to reset the BIOS option to Normal Boot is unplug your computer while it is running and allow it to completely shutdown (i.e. unplug and wait until everything is dark and the fans aren't running). If you are using a UPS ( battery powered uninterruptible power backup) then you'll need to temporarily use the wall socket instead for this to work (unless you unplug from the UPS, but if yours is like mine it's kinda hard to easily access the plugs in the back ... what you don't want is the computer continues to run off the UPS, we want it to crash). Plug the power cord back in and then when you reboot be ready on the Delete key as soon as you hit the power button to reboot. This will hopefully bring you to the BIOS setup screen (go back to section 2-1 if you had to skip ahead).
After we're all done I'll give instructions on getting Fast Boot re-enabled (optional).
"2-5 Peripherals
Intel Processor Graphics
Enables or disables the onboard graphics function. (Default: Enabled)"
Ahh ... finally to the meat of the matter!!
Now I'm not 100% sure what exactly will be highlighting once you get to this section (meaning will the words Intel Processor Graphics be highlighted or will Enabled be highlighted) but you'll hit Enter to change the setting once you get the highlight moved to where ever it goes. That will bring up a submenu that will allow you to select either Enabled or Disabled (use your arrow keys to move the highlight from one to the other ... we obviously want Disabled) and then hit Enter again to accept the change and close the submenu. You should now see that Disabled is the option shown under Intel Processor Graphics.
"2-7 Save & Exit
Save & Exit Setup
Press <Enter> on this item and select Yes. This saves the changes to the CMOS and exits the BIOS Setup
program. Select No or press <Esc> to return to the BIOS Setup Main Menu."
You can navigate to this section using the arrow keys or you could just hit F10 which should bring you to this section, probably with the Save and Exit confirmation submenu selected (if it doesn't Enter opens the submenu once the highlight is on Save & Exit Setup). Enter will save the changes and start a reboot.
I'd suggest letting the reboot go through and confirming that turning off the Intel Graphics solved your initial gray screen problem. If you decide that you want to re-enable the Fast Boot it's just a matter of opening the BIOS setup screen again and then navigating to section 2-4 and changing the Fast Boot to Enabled (same way ... move the highlight to Fast Boot, hit Enter and change Disabled to Enabled and hit Enter again ... F10 Save and Exit and let it reboot).
Now I know there's a lot of info here. Read through it and ask questions first ... there will still probably be things that you're not sure of. If you run into anything take note (write down) everything that's shown on the screen, navigate to the 2-7 Save & Exit screen and select Exit Without Saving. I'm pretty sure you can F10 then hit Esc and then arrow down to Exit Without Saving hit Enter and then accept Exit Without Saving by hitting Enter again. Your machine will reboot with all your BIOS settings left the same as they were. Post back here with your question.