Ubuntu 12.04 with Linux 3.5.0-39-generic has issues booting

Ubuntu 12.04 with Linux 3.5.0-39-generic has issues booting

I've been trying to get this working for days now and none of the posts
I've found on this site (or any other) have been able to help me fix this,
so sorry if this is a repost. I'm currently trying to dual-boot Windows 7
and Ubuntu on a desktop with a Gigabyte Z87N motherboard and an NVIDIA
GTX760 video card. When I try to boot Ubuntu "normally" (not in recovery
mode) I'm left with a blank screen with a blinking underscore. If I try to
run in recovery mode, then I get a lot of text output and then this:
[ 4.429609] [drm:drm_pci_agp_init] *ERROR* Cannot initialize the
agpgart module.
[ 4.429667] DRM:Fill_in_dev failed.
The system always comes to a complete halt (and again a blinking
underscore at the bottom of the screen) after those two lines print.
Sometimes, more lines print after that, but they always vary and dont seem
to be part of the problem (they seem to just be normal messages about
other drivers loading).
I followed these instructions to install my nvidia drivers.
but that didn't work (obviously). Pleeaaase help me. I know that the two
error messages above have been addressed before, but I haven't found any
fixes that work.
I've tried to boot with the "nomodeset" option but that doesn't seem to
change anything. I've also tried to boot with "text nomodeset" and gotten
the same results.
I forgot to mention that this all happens when I use the HDMI port on my
graphics card. If I use the HDMI port on my motherboard, Ubuntu boots just
fine. Another interesting thing I noted is that I don't see the
motherboard logo or the grub menu (where I choose between Ubuntu and
Windows) if I use the motherboard's HDMI. The screen just stays completely
black until I see the Ubuntu login page.
Also, I have an entry in grub called "Previous Linux versions" which lets
me boot into Linux 3.5.0-23-generic. I would boot into recovery mode here
before and it used to work, but for some reason even that doesn't work
now.
Sorry for the unorganized post...I'm not sure how to organize all this
random info that I have. Please let me know if you need any more
information, and thanks in advance if you can help me!