Mac Pro 3.1 not booting anymore

Circa 12 hours ago, I've made it to first install Snow Leopard on my Mac Pro 3.1, and, using BootCamp, I put Windows 7 64-bit on it and made it my default boot partition. After installing a few simple programs on it (VLC, Firefox) plus a few automatic Windows updates (whereupon it crashed one time which made the update process a bit more difficult), I decided to migrate data from another computer on an external disk to use on my Mac Pro.

Considering it wouldn't take long, I just plugged in the monitor and keyboard + mouse into the other computer without shutting my Mac Pro off. Turned out that it did take a bit longer than I'd expected for the files to get transferred from my other comp to the external disk...8 hours, to be exact.

When I then switched everything (Monitor and keyboard) back and tried to wake Windows 7 on my Mac Pro up from "sleep" aka "standby", I found out that it had obviously crashed and didn't respond. Screen stayed black. So I used the front button on the tower to boot it. Ever since then, the machine just plain refuses to boot up.

When I'm trying to use the Windows partition, the Windows DVD, or the "EPI" option when using the option key, what I'm getting is a screen (white text on black screen, with very nasty green stripes all over the screen) similar to the one giving me the option of "save mode", only that it's telling me that Windows fails to start entirely, and I can choose either "try start Windows again", or run some diagnoses for hardware failures. Trying again will give me the very same screen again. The diagnosis tool looks like the Windows install screen again, with very low resolution and wrong aspect ratio. Diagnosis tool is telling me that it can't solve the problem, which is that it's suddenly missing "hardware support" or "drivers" in order to boot.

Next, it offers me to go back to a previous state of my Windows installation (similar to Time Machine in MacOS), but no matter which one I click, I'm getting the error that it can't reset the system to any of those earlier times as it's getting no access rights. At least I can see there that the last updates made to Windows, next to a few last automatic Windows updates, consist of DirectX9 and Nero 9 (the latter reading on the box "now with Windows 7 support!", but it doesn't say anything about support for 64-bit). If it's not the long sleep state, I wonder if any out of those two could be the culprit.

On the other hand, if I'm using the option key on boot in order to boot into my Snow Leopard partition or boot from my Snow Leopard DVD, all that happens is that the entire machine freezes on that grey BG with the Apple logo and the spinning clock symbol that just freezes right in the middle of its rotations.

So that's what I got now. Windows partition won't boot. Windows DVD won't boot. Snow Leopard partition won't boot. Snow Leopard DVD won't boot. I've tried resetting my SMC, but still the same.

What do I do now? Am I now in possession of a large chunk of newly bought scrap metal?