Windows won't boot - stalls before login/welcome screen

A short intro (skip if you like):

Hi everyone, this system has been running close to 24/7 since roughly two years ago. A custom RT7Lite disc was used and a lot of tweaking has been done, so the system is well in need of a fresh format. Unfortunately, this was planned for after the holidays, and as I was unprepared for this crash, it could take me longer to figure out what I need to transfer to a new install then it would to fix the current one. Any suggestions will be greatly appreciated!

System specs:

OS: Win7 Pro x64
CPU: Intel Q9550
Motherboard: Gigabyte EP45-DS4P
Memory: 8GB PC2-8000
Graphics Card: ATI HD4870 (PCIe/512MB)
System Drive: 2x Intel x25-V SSDs in RAID0 (via mainboard's ICH10R)
Network: Intel Gigabit CT PCIe card
Firewall: Outpost Pro

The current problem:

System passes POST, bootloader, "Windows is Starting" animation. USB devices initialize, and the mouse pointer appears. The screen remains black (no background, login dialog, accessibility/power buttons, etc.) indefinitely. The mouse still moves and NumLock can be toggled, so the system has not halted - it just doesn't get any further than that. After 15 minutes power-saving kicks in and the display goes to sleep - Moving the mouse or pressing a key turns it back on again as though everything is normal, but it's still stuck at the black screen.

Events leading up to this:

I have been using a PCIe JMicron-based SATA card with a broken eSATA port, and I recently got an ASM1061-based SATA 6Gbps card to replace it. This new card is PCIe 2.0 and my motherboard only has two 2.0 slots - the x16 and x8 slots meant for video - so I was testing what difference it made running my gfx card in x8 mode. I decided running it this way was OK, so I started tweaking the SATA card. I had seen reports that using the generic Microsoft driver with this chipset was hugely detrimental to write performance, so naturally I tried to install the newest ASM one. This didn't work, as Windows told me "this location does not contain information about your hardware". I resorted to using the driver's installer program, which ran perfectly - but Windows kept using its own driver anyway.

Finally, I decided to try the older version of the ASM driver. This installed properly and the device was no longer listed as a generic ATA controller. On a hunch, I tried updating the driver again (without rebooting) to the newest driver, and Windows accepted it with no complaint this time. However, my firewall (Outpost) asked me whether I wanted to allow direct disk access to an uncertified/??? driver. I affirmed this as it was intended. It's worth mentioning that Outpost was being a nuisance when I was testing PCIe slots, as it wiped its configuration file each time I moved my NIC. This meant it lost all the rules regarding which system components were allowed to do what, and had me confirm each one.

I then rebooted to MS-DOS on a USB stick to update the SATA card's firmware. I restarted into Windows several times without issue, but the SATA card didn't show during POST or in the Device Manager. Turns out the uploader mislabelled a BIOS OROM module as the add-on card's firmware. Back in DOS, I flashed the correct/original file, but the card still didn't seem to work (no BIOS info page, still absent in Windows) so I went back and flashed it a third time. After that theBIOS splash screen re-appeared and it seemed like everything would be fine.

However, upon booting into Windows, I was now getting a consistent BSOD: STOP 0x00000024 0x0000000000190494 (I only have the first two numbers, which I googled on my phone out of curiosity). I rebooted to safe mode and the same BSOD came up after CLASSPNP.SYS was listed. At this point I inserted my Windows DVD and ran the Startup Repair function, which took a while but completed successfully. I checked the log after it was done and the only reported issue was that the 100MB System Reserved partition was "corrupt". After restarting, the BSOD is gone but I now have this black screen/no login issue.

Things I have tried:

-Pretended the login screen was there (entered password and pressed Enter) in case it was a graphical glitch.

-System restore is disabled so I can't use that to revert whatever caused this.

-Tried booting in each of Windows' alternate modes (VGA, Safe, Safe w/LAN, Safe w/CMD, Last Known Good, etc.), problem persists.

-Unplugged secondary display in case it was drawing stuff on the wrong monitor.

-Shuffled the expansion cards back to where they were when the problem started, tried alternate locations, booted with all cards removed.

-Opened a command line window from the Win7 DVD and ran SFC and scandisk. SFC reported there were several errors that could not be repaired, however this was also the case several weeks ago when I used SFC to troubleshoot an application. I'm fairly certain this can be blamed on the RT7lite'd install source.

-Booted into an old install of Vista x64 Ultimate on another drive, and replaced all instances of the ASM drivers with the older version. No change. Went back into Vista and renamed the driver files - no change.

Brainstorming:

-Non-destructive "Upgrade" install over existing version Has to be done from within Windows 7. Tried initializing this from Vista, but it seems it can only be installed over the currently active partition (and can't be done anyway because Ultimate trumps Professional.)

-This xbootmgr tutorial helped me narrow the timing of the problem down, it seems to be happening in the SMSSInit phase of MainPathBoot... Knowing this hasn't really helped me so far and it appears xbootmgr has to be initialized from the OS being traced, so I'm not sure if I can even use this tool.

-The automatic Startup Repair script (on the installation disc) reports that the system booted successfully. Running SFC without the /offwindir and /offbootdir switches reports that a system repair is pending. The bootloader lists the OS as "Windows 7 (recovered)"