Ubuntu 12.04.5 (32-bit) Guest Reaches GRUB, Doesn't Boot

[Hello World]

Host Specs
Windows 8.1 64-bit
AMD FX-6300 Six-Core
16 GB RAM
1 GB Nvidia GeForce GTX 750

If I left anything vital out, let me know.

VirtualBox 5.0.0-101573
The last thing I did before my Ubuntu 12.04.5 guest stopped booting properly was updating VirtualBox to the new 5.0 release and installing the updated Guest Extensions. Ever since then, the guest goes to GRUB, and attempting to boot normally or into recovery mode causes VirtualBox to throw out a critical error and power off the VM. I think I may have shut down the host for updating around the same time without shutting down the VMs first, so that could've broken something.

I've tried using the testbuild VirtualBox-5.0.0_RC3-101495-Win, but that doesn't appear to change anything. I would really like to get it running again, or at least recover my files if I have to make a new VM.
I have also tried downgrading to my old 4.3.28 VBox installation, but that just made the Ubuntu machine and another VM inaccessible, though the accessibility problem was fixed after going back to 5.

Anyway, I attached my log and png file. Both are from my most recent attempt at a recovery mode boot, as the PNG supplied from the normal boot attempt showed an empty black screen, while the recovery attempt at least managed to print something to screen before the whole thing crashed.

EDIT: Okay, I just made a new VM telling it to use that same .vdi file, and it booted up. Networking is broken right now, but I'm glad it booted up at least. The only differences between the original and the new VM apart from some USB filters is below:

Original (doesn't boot)
Ram: 512 MB
Virtualization: PAE/NX

New One (same vdi, boots)
Ram: 768 MB
Virtualization: PAE/NX , KVM Paravirtualization

[Perryg]

If you fix this

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00:01:02.208588 HM: HMR3Init: Falling back to raw-mode: AMD-V is disabled in the BIOS (or by the host OS).

It should fix this

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Guru Meditation -2403 (VERR_TRPM_DONT_PANIC)